Table of Contents
1996-1998 I-APS Officers
Thomas J. Meyer
Professor Thomas J. Meyer of the University of North Carolina, Chapel Hill, is the winner of the
1997 I-APS Award in Photochemistry. He receives the award in view of his innovative work on electron
transfer phenomena, radiationless decay processes in metal complexes, photoelectrochemistry and
designing systems that produce a charge separation. Largely as a result of his efforts, rational
tuning of the excited states in metal complexes is now possible. Aside from his pioneering
research accomplishments, Tom has been a regular at IAPS meetings and, as one of the
supporting letters stated: "a consummate repesentative of inorganic photochemistry".
Join us in honoring Tom at the Winter Conference in Clearwater Beach, Florida (January 1-5, 1997).
Report on the 8th I-APS Meeting, Foz do Iguaçu, Brazil
Russ Schmehl, Department of Chemistry, Tulane University, New Orleans, LA
The eighth meeting of the society was the first outside the United States and those who attended
were treated to both a stimulating, truly international meeting and the wonders of a genuinely
spectacular setting. The attendance for the conference exceeded 200 and was the largest of any
IAPS conference to date. It was also the first to be held in the spring / fall (Southern Hemisphere),
May 19 - 24. Before discussing the meeting program it is imperative to recognize the extraordinary
efforts of the persons most directly responsible for the success of the meeting: Frank Quina
(USP, São Paulo, Brazil) and Dick Weiss (Georgetown, Washington DC, USA). They not only
found the site for the conference and made the detailed arrangements, they also helped others
sort through the visa procedures and dealt with an endless string of questions that kept their
internet mailboxes stuffed in the weeks preceding the conference.
The meeting featured a mix of speakers from North (21) and South (10) America as well as two European
speakers. In addition, there were two poster sessions with 111 total contributions. The sixteen plenary
lectures were spread over the five days of the meeting. The first was given by Eduardo Lissi (Santiago, Chile)
on applications of chemiluminescence in biological chemistry. He illustrated how chemiluminescence could
be used as an analytical tool in evaluating peroxyl radical induced chemiluminescence and the quenching
of this luminescence by the addition of antioxidants. This was followed by a short talk by Russ Schmehl
(New Orleans, LA, USA), discussing electronic coupling in intramolecular electronic energy transfer
between Ru(II) diimine donors having triplet MLCT excited states and pyrene linked by a single C-C bond.
The morning session continued with a contribution by Bob Liu (Honolulu, HI, USA) in which he illustrated
elegant molecular design of bacteriorhodopsin and sensory rhodopsin analogs which absorb at longer
wavelengths than the naturally occuring systems. He reported an azulenic derivative which, upon association
with apobac- teriorhodopsin, formed the first near infrared absorbing (830 nm) bacteriorhodopsin analog.
The morning concluded with a talk by Wilhelm Baader (São Paulo, Brazil), examining the reactivity of the
chlorophenyl ester of monoperoxyoxalic acid, a potential intermediate in the peroxyoxylate chemiluminescence
system. It was found that the monoperoxo compound cannot be an intermediate in the system since it
undergoes a cyclization reaction prior to interaction with activator dyes.
The afternoon session began with three short talks involving the photophysics and photochemistry of
aromatic hydrocarbons. Tony Testa (Jamaica, NY, USA) discussed his continued studies on the
photophysical behavior of phenylpyridines. Fluorescence quenching studies indicate the singlet
excited states are quenched by proton transfer and AM1 semiempirical MO calculations suggest
that the triplet excited state of 4-phenylpyridine is nearly planar. This was followed by talk on the
photochemical behavior of tetracene adsorbed on silica at varying surface coverages by
Reza Dabestani (Oak Ridge, TN, USA). He found that dimerization occurs on deoxygenated, dry
silica even at low (<1 % of monolayer) coverages but that photooxidation occurs in the presence
of air to yield mainly the 5,12-endoperoxide. The reaction was also found to occur in the absence
of irradiation. The session concluded with Fergus Gessner (São Carlos, Brazil) presenting his group's
work on the thermal and photophysical behavior of p-terphenyl adsorbed on various clays.
Fluorescence was observed in the absence of quenching impurities (i.e. Fe3+ in Wyoming montmorillonite)
in the clay and excimer emission is observed at high coverage. In addition, evidence for cation radical
formation was obtained in some clays.
Oral presentations for the first day concluded with plenary lectures by Marcello Gehlen (São Carlos,
Brazil) and Irene Kochevar (Cambridge, MA, USA) and a short talk by Juan Cosa (Rio Cuarto,
Argentina). Gehlen's talk focused on understanding the dynamics of sensitized radical ion initiated
polymerization of styrene derivatives in the presence of reverse micelles. It was shown that inclusion
of the sensitizer and initiator in the water pool of the reverse micelle dramatically increases the
efficiency for photoinitiation of polymerization by effectively eliminating sensitizer quenching
by the substrate monomer. Cosa followed this with a discussion of pyrene/ dimethylaniline exciplex
formation in AOT reversed micelles and BHDC/benzene/water microemulsions. Kochevar
finished the day's talks with an elegant presentation on rose bengal (RB) sensitized photoprocesses
in cell plasma membranes. The key result is that the reactive intermediates produced depend on
the photolysis wavelength and the intensity of excitation. Radical or radical ion species result
from two photon excitation of RB to produce membrane damaging species. The activities of the
first day concluded with a lively evening poster session.
The second day opened with a lecture by Peter Wan (Victoria, BC, Canada) on the reactivity of
quinone methides generated by photolysis of hydroxy substituted benzyl alcohols. Reactions
of the quinone methides include cyclization of o,o'-biaryl substituted derivatives and dimerization
of m-quinone methides. Denis DeKeukeleire (Ghent, Belgium) followed with elegant demonstrations
of regio- and stereoselective intramolecular arene-alkene photocycloadditions. Focusing on
photoreactions of 4-phenoxybut-1-enes, they have found examples of cycloadditions which
yield products with as many as six contiguous chiral centers. The emphasis shifted to
isomerization reactions with talks by Pedro Aramendia (Buenos Aries, Argentina) and
Jack Saltiel (Talahassee, FL, USA). Aramendia's lecture focused on the isomerization
of carbocyanines as a system for comparing the dynamics of rotation, monitored by
fluorescence anisotropy, and isomerization. The two processes have different viscosity
dependences and it was concluded that the effect arises because of a difference in the
time scales of the two processes. In Saltiel's presentation he showed how principal c
omponent analysis could be used to resolve fluorescence spectra of geometric isomers of
trans-1-(2-anthryl)-2-phenylethene. PCA was applied to sets of spectra obtained with varying
concentrations of the quencher fumaronitrile; the approach also was used to extract two
components, S2S0 and S1S0, from the temperature dependence of the emission of one isomer.
The second afternoon session began with a talk by Josh Goodman (Rochester, NY, USA) in
which he illustrated a alternative approach to defeating energy wasting back electron transfer
in photoinduced electron transfer reactions by devising systems in which the return electron
transfer results in bond dissociation. The system used to illustrate this approach was 1,2-diphenylcyclopropane
with various photooxidants. Marshall Wilson (Cincinnati, OH, USA) then discussed the
formation of aryltetralin derivatives via the 2+2 photodimerization of covalently tethered
bis-cinnamates followed by oxidative rearrangement of the intermediate truxinic acid derivative.
The rearrangement was accomplished using either thermal oxidants or via photoinduced electron transfer.
The remaining afternoon talks dealt with new experimental approaches for extracting
photophysical information. Joel Harris (Salt Lake City, UT, USA) began the session
with a presentation on the use of photothermal methods, in particular transient thermal
lens spectroscopy and transient photothermal grating spectroscopy, in examining
second and mixed order reactions of aromatic ketones. In addition, he presented a
clever approach to extracting Raman spectra of transient species from the intensity
dependence of Raman spectra collected directly from an excitation pulse; the excited
species has a higher order dependence on laser intensity than the ground state.
Malcolm Forbes (Chapel Hill, NC, USA) followed with a talk on dynamic behavior of
radical pairs, either flexible biradicals or micellized radical pairs, which are generated
from the photolysis of either cyclic or amphiphilic ketones. Using time resolved epr
spectroscopy to examine chemically induced dynamic electron spin polarization, the
Forbes group found that the radical pair mechanism appears at early times and evolves
into spectra representative of a spin correlated radical pair mechanism for micellized
amphiphilic ketones. Jeff Zink (Los Angeles, CA, USA) then showed how resonance
Raman, emission and absorption spectra and Heller's wavepacket propagation theory
could be used in detailed evaluation of excited state distortions of relatively simple
transition metal complexes.
The evening of the second day featured the second poster session. The session, complete
with cash bar, proved once again to yield lively discussions and healthy profits for the hotel bar.
The next day began with Mitch Winnik (Toronto, ON, Canada) who discussed applications
of luminescence techniques to the analysis of two types of block copolymers : those which
form separate into distinct microphases in the bulk and those with two hydrophobic segments
capping a central hydrophilic portion. The latter copolymers aggregate in solution to form highly
crosslinked micelles and luminescence quenching studies were effective at providing a measure
of the aggregation characteristics of the micelles. The topic of organic photophysics in
polymeric media continued with a talk by Teresa Atvars (Campinas, Brazil), who discussed
effects of stretching the host polymer matrix, low density polyethylene, on anthracene
fluorescence. Arrhenius like plots of the decrease in fluorescence intensity with increasing
temperature led to the conclusion that the measurements provided a measure of the conformational
mobility and diffusional motion of polymer chains. The photodecomposition of polymers was
addressed by Graciela Blanchet (Wilmington, DE, USA). She showed that laser ablation of
various polymers leads to pyrolitic decomposition of the polymer, although often the same
products cannot be obtained by direct pyrolysis; the polymer vapor can be deposited on
surfaces and has been shown to repolymerize. The laser ablation/deposition technique can in
principle be used for imaging films for various applications. The morning session was completed
with a talk by Elsa Abuin (Santiago, Chile) on the effects of urea, at relatively high concentrations,
on various photophysical processes in micellar media. Photoprocesses examined included pyrene
fluorescence quenching by oxygen in SDS, quenching of polycyclic aromatic hydrocarbon
luminescence by various micelle counterions and ANS fluorescence quantum yields and
lifetimes in SDS micelles.
The afternoon featured an outing which included a tour of the local surroundings.
Foz do Iguaçu is located essentially where Argentina, Brazil and Paraguay meet and
is the site of a truly magnificent waterfall consisting of 275 total falls spaced over
approximately 3 km and averaging 80 m in height (wider than Victoria and higher than
Niagara). The falls are genuinely spectacular, in part because they span such a tremendous
area and a bit because Brazilians are not so paranoid about safety so that there are fantastic
walkways allowing visitors to walk out over the precipice of several falls. In addition, we
were treated to a motorized raft ride from below the falls up the river to the base of the falls;
this experience may well be the lasting memory of the conference for many.
The next morning we returned to business with a lecture by Heinz Roth (New Brunswick, NJ, USA)
on the structure and reactivity of radical cations generated from photoinduced electron transfer
reactions of strained ring systems containing olefinic fragments. Radical cations were characterized
using CIDNP spectroscopy and ab initio calculations. Reactions of the cation radicals included
capture of nucleophiles, deprotonation and rearrangements. This was followed by a talk by Herbert Meier
(Mainz, Germany) on the topic of annulene photodimerization to form structures which have been
dubbed belt cyclophanes. The structures result from three successive 2+2 cycloadditions between
the two ring structures and the photoreaction occurs in very dilute (micromolar) solutions.
Keith Horn (Morristown, NJ, USA) then discussed the photochemistry of various secondary
aliphatic amides with an emphasis on oxidative degradation processes. For example N-pentylhexanamide
was shown to yield hexanamide upon photolysis in oxygenated solutions via an alpha-hydroperoxide
intermediate. Unusual chain length dependence was observed in the quenching of xanthone triplets
by a series of secondary aliphatic amides. The morning session concluded with a talk by Rosa Erra-Balsells
(Buenos-Aires , Argentina) in which she outlined the factors influencing the effectiveness of various matrices
in generating ions for matrix assisted laser desorption ionization time of flight, MALDI-ToF mass spectrometry.
It was found that protonation of analytes by charge transfer is the main path for ionization induced by
matrices which contain both hydroxy and carboxyl functionalities.
The afternoon began with an overview of the past 35 years of photochemistry by one of the few people
able to comment on the subject from personal experience : George Hammond (Bowling Green, OH, USA).
In his talk Hammond marveled at the advances in technology that have been applied to photochemistry,
recognized areas which have sprung up out of the early work and applauded those continuing to work
on fundamental aspects of light induced reactions. R. Srinivasan (UVtech, Ossining, NY, USA) then
continued with a discussion of applications of ultraviolet lasers to ablative photodecomposition processes.
Such processes have found widespread application areas as diverse as dry etching processes and corneal
surgery. Excimer laser intensities of greater than 1 megawatt per square centimeter are required before
ablation occurs. At these intensities the absorption process is a two photon process. The final talk of the
day was given by Elizabeth Morolino (Bowling Green, OH, USA), winner of the Closs Student Award.
In her talk she very elegantly illustrated the link between intersystem crossing processes from LMCT
states of M(II)-NO porphyrin complexes (M = Fe, Co) and quantum yields for NO photodissociation
from the complexes. The Fe(II) complex has a higher intersystem crossing yield and a lower quantum
yield for NO loss.
As with many meetings of this type the last evening was occasion for a banquet celebration. This particular
banquet, however, was a lavish and thoroughly enjoyable affair that will certainly live long in the memories
of those who attended. The banquet was complete with music, dancing (yes, even the gringo's did their
best...with Dave McMillin leading a line dance) and general merriment that lasted into the wee hours,
long after this gringo succumbed to exhaustion.
The final morning of the meeting was greeted with a remarkably well attended (considering the
previous night) talk by Kerry Thomas (South Bend, IN, USA) in which he presented results of laser
flash photolytic studies of solutes incorporated into porous solids. With numerous solutes
photoionization readily occurs. Ira Brinn (Rio de Janeiro, Brazil) then discussed excited state
proton transfer reactions of 2,3 and 2,7 naphthalenediols. Kinetic analysis of single photon
counting results for the diols indicated that excited state proton transfer rate constants were
lower than for simple naphthols, the effect being larger for the 2,3 diol dissociation.
Since inorganic chemists are in general good natured, the final two talks of the meeting were given
by two fine photochemists from the inorganic community: Tom Meyer (Chapel Hill, NC, USA) and
Alistair Lees (Binghamton, NY, USA). Meyer presented work of his group focused on understanding
light induced energy and electron transfer reactions in complex assemblies, such as polymers and
peptides labeled with varying ratios of donor and acceptor moieties. The work discussed included
studies of long range triplet energy transfer and inverted region electron transfer. Lees finished
the meeting with a presentation on C-H activation upon photolysis of hydrido Rh(I) pyrazoylborate
complexes in hydrocarbon solvents.
Overall the meeting was a great success. It was the first I-APS conference not held in the winter
and the first held outside the United States. It represented a huge effort by both the local organizers
and the program organizing committee and they should be commended for putting together a truly
memorable conference.
XVIth IUPAC Symposium on Photochemistry, Helsinki, Finland
Communicated by
The XVIth IUPAC Symposium on Photochemistry was held during the third week of July in Helsinki, Finland.
The participants were welcomed to this beautiful and sunny city by a reception party on Sunday
evening at the University of Helsinki. The scientific program was initiated on Monday morning
in the University's Great Hall, with the introductory plenary lecture presented by Professor W. Adam
on the elucidation of electronic substituent effects in radicals, triplet diradicals and higher spin states
through application of EPR and time-resolved absorption techniques. The following session
featured presentations by M. Platz, on the photochemistry and rearrangements of alkyl carbenes,
G. Lodder, on recent developments in the generation of radical cations from vinyl halides,
and E. Hilinski, on the use of heavy atom effects in picosecond time resolved, mechanistic studies
of bond photodissociation. After lunch, J. Michl presented the second plenary lecture on the
subject of spin orbit coupling in biradicals and the insights which theoretical studies can provide.
The final presentation of the day, from H. Roth, provided the audience with numerous demonstrations
of radical cations as intermediates in the photochemistry of strained ring and unsaturated bifunctional
systems. The remainder of the afternoon on Monday, along with two hour blocks on Tuesday,
Wednesday, and Thursday afternoons, was devoted to poster sessions. More than 350 papers
were presented which covered a very broad range of fascinating problems in photochemistry.
The four poster sessions gave conference participants ample opportunity to read and discuss the
posters with the presenters, as well as to engage in informal discussions with all the participants.
The scientific program on Tuesday started with a plenary lecture by J. Troe who described the physical
processes underlying photoisomerization reactions in different phases. This lecture was followed
by a presentation from M. Klessinger on the role of conical intersections in determining
selectivities in singlet and triplet reactions. After a coffee break, presentations were made in
three, parallel sessions. One session presented studies of the photochemistry and photophysics
of biological molecules and supramolecular structures with presentations by G. Orrelana on
mechanistic studies of nucleotide quenching of excited viologens intercalated into DNA,
followed by H. Tamiaki who discussed energy transfer in chlorin aggregates as models
of photosynthetic antennae, N. Gfeller who discussed energy transfer in dye loaded zeolites as
model antenna systems, and X. Y. Lauteslager who demonstrated the effects of flexibility
on the photophysics of bridged donor acceptor compounds. The second session covered
technological applications of photochemistry with presentations by C. Decker on novel
photoresists for high-speed laser imaging, F.C. De Schryver on submicron photochemistry
and photophysics, J. Ph. Soumillion on potential applications of fluorophores covalently
grafted to silica surfaces, and J. Zhao on visible light induced degradation of dye pollutants
in TiO2 aqueous dispersions. The third session covered inorganic aspects of photochemistry
with talks by V.F. Plyusnin on the involvement of Pt(III) intermediates in the photochemistry of
PtCl62- with amino acids, M. Pettersson on photoproduction of rare
gas compounds in solid Xe and Kr, T. Szymanska-Buzar on the involvement of catalytically important
intermediates in the photoreactions of group 6 metal carbonyls, and M. Litter on photosensitization of
TiO2 by hydroxoaluminum tricarboxymonoamidephthalocyanine. The afternoon on Tuesday
was devoted to the poster session and an excursion.
The plenary lecture on Wednesday morning was presented by K. Wentrup on the mechanism of
3-diazo-4-pyridone photolysis. J. R. Scheffer followed with a presentation on structure-reactivity
relationships in photochemical reactions in crystals. Once again, oral communications were presented
in three parallel sessions. In the first session T. Fiebig discussed electronic coupling and orbital
symmetry effects in electron transfer reactions of flexible, short-linked donor-acceptor-systems. The
next presentations were by L.G. Arnaut on theoretical models for electron transfer reactions,
followed by M.G. Kuzmin's presentation on the role of low polar exciplexes as intermediates
in excited-state electron transfer reactions, and a talk by A.R. Eremenko on electron transfer
and exciplex formation in heterogeneous media. The first talk in the second session was given by
L. de Cola who described the use of rigid donor acceptor metal complexes in studies of energy
and electron transfer. This lecture was followed by Y. Eichen's presentation on reversible,
photoinduced and thermally activated proton-transfer processes in solid systems, followed by
C. Bohne's talk describing the use of excited triplet states as probes of dynamic processes in
cyclodextrin complexes and bile salt aggregates, and R. F. Khairutdinov's presentation on models
for bimolecular reactions on the surface of nanoparticles. In the third parallel session H. Koshima
described how absolute asymmetric syntheses can be effected in two component crystals,
H.E. Zimmerman discussed recent advances in the application of computational methods
to mechanistic organic photochemistry, W.M. Nau presented results of picosecond time-resolved
experiments which demonstrated efficient radiationless deactivation of excited singlet states in intermolecular
hydrogen abstraction reactions, and M. Shah described time-resolved studies related to the photochemistry
and photoinitiation activity of 2-substituted anthraquinone derivatives. The afternoon on Wednesday
was devoted to three parallel workshops entitled Time-resolved structural changes obtained from photothermal
studies in solution, Photochemical methods for the oxidative degradation of organic pollutants, and Photopolymerization.
All the workshops prompted considerable speaker and audience participation. The photothermal workshop,
chaired by S. Braslavsky, featured six presentations. T. Gensch described the time evolution of
photoacoustic signals arising, principally, from volume changes. R.J.D. Miller described transient
grating investigations of energy transduction and structural relaxation as related to protein function. R. Schmidt
described photoacoustic calorimetry studies directed toward determination of volume changes in photodissociation
reactions. E. Vauthey described the application of transient thermal phase grating methods to the
determination of electron transfer kinetics and the time evolution of transient spectra. C. Viappiani described
studies of volume changes accompanying proton transfer reactions and M.B. Zimmt described potential
problems in separating volume and enthalpy contributions to photothermal signals generated in organic solvents.
The workshop on Phototreatment of Waste Water featured introductory presentations by J. R. Bolton
on the use of light driven oxidation of organic pollutants in water and by E. Oliveros on large scale
development of light enhanced Fenton chemistry for water purification. The photopolymerization
workshop was organized and directed by K. Dietliker and D.C. Neckers. D.C. Neckers provided a
general introduction on radiation curing and its industrial applications. This was followed by K. DietlikerÕs
brief overview of currently available U.V. and visible light photoinitiators for use in radical polymerization
and C. Decker's presentation of new methods for on-line monitoring of the curing process.
The participants agreed that development of more efficient photoinitiators and raw materials, optimization
of formulations through the use of new analyzing techniques as well as recent developments in light sources
will open new applications for radiation curing in the near future. Continued strong growth of photopolymerization
applications in industry is to be expected.
On Thursday morning, the plenary lecture by M.A. El Sayed presented fascinating insights into the
molecular mechanism by which Bacteriorhodopsin converts light into chemical energy. The following presentation,
by M. Goeldner, described the use of photolabile molecules to probe and to modulate enzymatic a
ctivity of cholinesterases. He also presented a strong case for the utility of time-resolved, macromolecular
crystallography in such studies. H. Tomioka followed with a presentation on the reactivity of ortho-quinoid
compounds as determined from matrix isolation studies. In the first of three parallel sessions, B. Kozankiewicz
described how the zero-field splitting in the T0 and T1 states of 2-naphthylphenyl
carbene could be determined from fluorescence hole-burning studies. F. Lahmani followed with a
discussion of how chiral discrimination could be effected using laser induced fluorescence of clusters in jet
cooled complexes, and I. Renge described applications of spectral hole burning in solid-state photochemistry
at low temperatures. In the second parallel session, K. Nakatani showed that derivatives of
dibenzoyl-diazomethane can photocleave DNA. The intermediacy of ketenes or carbenes was also discussed.
T.H. Koch presented recent developments and applications of halonucleotides for nucleoprotein photocrosslinking,
and C.A.M. Seidel described static and dynamic quenching of several dyes by nucleobase derivatives
and the importance of both processes for DNA sequencing by laser induced fluorescence. The third parallel
session was devoted to ultrafast processes. A.N. Macpherson presented femtosecond time resolved
fluorescence studies of carotenoids, followed by T.-H. Tran-Thi's presentation on the ultrafast dynamics
in the proton transfer reaction from excited pyranine to water, and D.N. Nikogosyan spoke concerning
the primary photochemical processes of concentrated aqueous thymine solutions. In the afternoon A. Osuka
presented a plenary lecture on the impact that structural features exert on photoinduced electron transfer
in synthetic porphyrin arrays. This was followed by L.B. Johansson's presentation of intricate mathematical
models for the description of energy migration and rotational motion within bichromophoric molecules. E. Chandross
chaired the evening discussion on the future of photochemistry. Several different points of view were presented
by the discussion panel, which included M. Irie, R.A. Caldwell, J. Michl, K. Dietliker, M. Goeldner and by
the audience.
The last day of the conference opened with F. Wilkinson's plenary lecture describing the intricate details
of quenching of electronically excited states by molecular oxygen. M.G. Neumann followed with a presentation
on the use of photochemical probes to study interactions between surfactants and polyelectrolytes. D. Stufkens
described the wide range of reactivities and lifetimes exhibited by several Re- and Ru-complexes. J. Kelly
presented results from studies of photoinduced electron transfer between ruthenium metal complexes or dyes to
DNA, and G. Marconi finished the morning session with a description of theoretical and circular dichroism
studies of cyclodextrin inclusion complexes. In the afternoon T. Basch presented single molecule spectroscopic
studies of spontaneous and light induced spectral jumps, and H. Shizuka
described the photophysics and photochemistry of triplet exciplexes involving naphthalene compounds.
The final session of the conference was devoted to the Porter award. Lord Porter presented the award to
N. Mataga. Lord Porter described the numerous and broadly distributed accomplishments of Professor Mataga.
In his lecture, Professor Mataga highlighted the development of exciplex chemistry over the course of his long and
impressively productive career.
In addition to the diverse and intense scientific program, a busy social agenda was also arranged. On Monday
the conference participants were invited to a reception, given by the city of Helsinki in the Town Hall, which is located
close to the picturesque Market Square. On Tuesday afternoon we were treated to a boat tour which featured the
beauty of the harbor and islands around Helsinki. During this tour we visited the Suomenlinna Sea Fortress and
learned some intriguing Finnish history. A wonderful chamber music concert featuring the "Ensemble Finlandia"
was held on Wednesday night in the Great Hall of the University. The finishing touch on Friday evening featured
a banquet at the Kulosaaren Casino.
We would like to congratulate Jacob Wirz, the chair of the international organizing committee, for orchestrating
a diverse and very interesting scientific program, and Helge Lemmetyinen, the chair of the local organizing
committee, for the wonderfully arranged facilities, the friendly and helpful staff, the fantastic weather and
for providing all of us with the opportunity to visit Finland.
Second International Symposium on 193 nm Lithography
Colorado Springs, Colorado, July 30-August 2, 1996
Elisabeth Morlino
Program
The second international 193 nm lithography symposium was held in Colorado Springs,
Colorado, from July 30 to August 2, 1996, at the Broadmoor Hotel located at the
base of Pikes Peak. The symposium cochairs, Dr. Masaru Sasago and Dr. David Shaver,
and the entire organizing committee did a wonderful job in putting together a very
interesting program in a beautiful location. Although the meeting was located in
the middle of some fabulous scenery the over 280 attendees from North America,
Europe and Asia did an admirable job in attending the scientific sessions.
The race for memory capabilities keeping up with technological advances in
computing has spurred the lithography community into developing new
processes to enable the production of smaller chips. Recently, rapid
development of microprocessors has also played a vital role in encouraging
the furthering of lithographic technology. The race now involves making chips
smaller and smaller invoking the need for higher and higher resolution in the
processes that are involved in making semiconductor chips. In order to keep
up with technological advances in computing, lithography will need to have
0.18 mm resolution by 1999. The lithographic techniques being pursued to
achieve this resolution are UV, E-beam and X-ray lithographies. Current UV
techniques involve using 248 nm lithography and improving resolution by
moving to using 193 nm lithography is appealing (and the industry is hoping, cost efficient).
In the pursuit of advancing 193 nm photolithography the approach is divided into
three distinct areas: mask technology, resist technology and hardware considerations.
Although the people who work in each area have highly focused goals everyone
seems very interested in what is happening in the other areas as well as their
own specialty. This attitude is very encouraging to an outsider and, no doubt,
increases the amount of interdisciplinary understanding...something we could
all do with more of.
The first session presented an overview of the considerations currently
under investigation in lithography at 193 nm. The current technology and
problems in each area were briefly discussed. The next session concentrated on
the optical materials, light sources and exposure tools proposed to be used in the
next of generation production machines. Concerns included laser source
performance which concentrated on linewidth, an important consideration
when considering 0.18 mm resolution. Other issues were substrate positioning
systems and their resolution as well as the optics used to deliver the 193 nm
beams to the substrate surface. The next topic focused on resist materials and
processes. The concerns in this area focused on the robustness of the resist to
etching techniques, resolution, photospeed, solubility, and process latitude.
The resist systems on the horizon consist of monomer backbones that have
side chain substituents chosen to provide a specific function. Current investigations
have concentrated on norbornene monomer systems and seem to have significant
promise. Later sessions focused on masks and mask technology. Concerns in this
area are focused on the robustness of the masks to 193 nm photons which, in turn,
focuses on materials, pattern generation and processing. The most critical mask
requirement at the current state of the art is feature size control. In addition to the
sessions covering the three subsections of 193 nm lithography technology
advancement there was a poster session which had contributions from the
three areas, and two workshops. One workshop focused on exposure tools
while the other consisted of a panel discussion covering single and multilayer resist systems.
Amongst all of this technology the organizers did give us an afternoon off to enjoy the
surroundings. While some elected to test their skills at the local golf courses the rest
of us tested the rapids on the Colorado river, an event not to be easily forgotten.
Prospects for Photochemists
There were several people interested to know why a spectroscopist interested in
fast photo-kinetics was in attendance at this meeting. Having explained my attendance,
the group was very informative as to why photochemists in general should be interested
in photolithography. They were very accommodating as to the exact nature of the problems
associated with photolithography as a whole and how an interested photochemist could
be a highly sought after commodity in the industry. The design of resists and their
practical implementation in lithography is a key problem in the advancement of the
technology. There were a very limited number of purely research-based people in
attendance with the resources needed to understand the resist problem on a
detailed level. Advancement of resist technology needs chemists with backgrounds
such that absorption of light and the processes pursuant to it can be understood on a
molecular level and can be related to the macroscopic system. Besides the macroscopic
problems associated with the resists in lithography there are some basic science questions
concerning electron and energy transfer in bulk materials as well as adhesion science.
There are also some materials concerns involving the optical delivery systems utilized
in 193 nm lithography. Photochemists interested in the interaction of light and bulk
materials could be helpful in designing systems that have superior functioning
capabilities. On the whole the prospects for employment of photochemists in
193 nm lithography research and development look good.
Although the current need for photochemists in developing photolithographic
techniques is obvious, the long term prospects (after 2015, for example) for such
people is uncertain in this author's opinion. The next step to obtaining better
resolution in lithography appears to be headed towards using electron- and X-ray
beams in place of UV systems. A photochemist's usefulness in designing hardware
and chemical systems for use with these sources is not inherently obvious.
Acknowledgments
The author would like to extend her thanks to Dr. R. Srinivasan and Sematech
for inviting her to attend the conference and for the funding necessary for the
opportunity. She would also like to thank Karen Brown for waiving the registration
fees for the meeting and to congratulate her on the superb organization and execution
of such a conference.
US - Latin American Workshop on Time-Resolved Techniques in Photochemistry, Photophysics, and Photobiology
Workshop held May 24-27, 1996, in Foz do Iguaçu, Brazil, under the auspices of the Divisions
of International Programs and Chemistry of the U. S. National Science Foundation (NSF)
and the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).
Workshop Organizers
Dr. Richard G. Weiss, Department of Chemistry, Georgetown University, Washington, DC, USA
The organizers wish to extend special thanks to the following people for their interest and professional
assistance in bringing this Workshop to fruition:
Dr. Frank Anger - Division of International Programs, NSF, Washington, DC
General Considerations
This Workshop brought together selected experts from the USA and from Latin America to discuss
mutual interests and problems in the area of the application of time-resolved techniques in
photochemistry, photophysics and photobiology. Secondary objectives included the
development of binational collaborations between U. S. and Latin American scientists.
The Workshop consisted of individual presentations by participants grouped into themes
that reflected the various facets of the Workshop topic. The presentations were intended to
emphasize, through specific examples, the manner in which time-resolved techniques can
be employed to obtain the desired scientific information, the deficiencies and limitations
imposed by the current capabilities of the techniques and potential near- and long-term
advances in instrumentation that will allow new scientific questions to be answered via
the use of time-resolved methodology. The theme group reports were intended to provide
summaries of the status of the various session topics in a form that can be disseminated to
the general scientific community.
Informal discussions, both within and outside the formal sessions, were strongly encouraged
and the format of the workshop was designed to foster and stimulate such interactions. The
extent to which the workshop accomplished its objectives ultimately depended on the
effectiveness with which the individual participants interacted and shared experiences
and knowledge.
Theme Sessions and Individual Presentations
Session 1: Time-Resolved Photothermal Methods.
Session 2: Time-Resolved Absorption/Emission Techniques.
Session 3: Time-Resolved Emission Techniques I.
Session 4: Time-Resolved Emission Techniques II.
Session 5: Specialized Time-Resolved Techniques.
Session 6: Time-Resolved Vibrational Spectroscopy.
Time-Resolved Vibration Spectroscopy
Peter Ford, Department of Chemistry, University of California, Santa Barbara
Time resolved techniques allow one to plot the temporal course of photochemical events, i.e. the rise
and fall of key species, excited state, reactive intermediates and final products. Vibrational detection
is particularly useful for spectroscopic characterization and kinetic studies of reactions since the
relevant compounds often include functional groups with characteristic frequencies which are
sensitive to molecular structure and conformation as well as the medium. The broad absorption
bands commonly seen for solution phase compounds by time resolved electronic spectroscopy,
generally allow little structural interpretation, and the bands of various species often overlap.
The much narrower vibrational bands give better resolution and often allow for direct observation
of temporal decay and appearance of individual species with minimal interference. Numerous
qualitative and quantitative criteria have been elaborated for the analysis of such bands in terms
of structure and bonding.
In the time-resolved Raman or TRIR spectroscopic experiments. The pump beam excites the initial
molecule from its ground electronic state to an excited state. The excited molecule relaxes, frequently
to the lowest vibrational level of the lowest electronic excited state of a given spin multiplicity, or
undergoes a chemical reaction to produce a new molecule. In both cases, the result of the pump
pulse on the system after vibrational relaxation has occurred is called the transient. The probe
pulse then is used as the source for obtaining the Raman spectrum of the transient. For the TRIR
experiment, the probe is either a CW IR source such as a diode laser or (for most ultrafast experiments)
an IR pulse formed by frequency difference methods.
TRIR systems can be separated into several categories. The first is the conventional pump-probe
system with a ns pump source, a continuous IR probe source operating at a single (but tunable)
IR frequency and a fast rise time, LN2 cooled diode detector. The advantage of this system is
relative ease of use. The second involves an ultrafast laser as the pump source and some sort
of IR pulse generated in conjunction with the excitation pulse with the temporal aspects
determined by small light pathlength differences. The obvious advantage is the much shorter time
intervals which may be probed. The third utilizes "step scan FTIR" detection technique has the
advantage of much easier data collection over wide frequency ranges. These are outlined in Table 1.
Letter from Dave McMillin, I-APS President
1997 I-APS Award in Photochemistry
Report on the 8th I-APS Meeting, Foz do Iguaçu, Brazil
XVIth IUPAC Symposium on Photochemistry, Helsinki, Finland
Second International Symposium on 193 nm Lithography, Colorado Springs, CO
US - Latin American Workshop on Time-Resolved Techniques in Photochemistry
Time-Resolved Vibration Spectroscopy
Time Resolved (CW) Electron Paramagnetic Resonance Spectroscopy
Photoexcited States of Buckyball-Based Materials (see hardcopy version)
Photochemical Reactions of Fullerenes (see hardcopy version)
Selective Photooxidation of Small Hydrocarbons by O2 in Zeolites (see hardcopy version)
Near Field Scanning Optical Microscopy/Spectroscopy (NSOM)
Upcoming Meetings
Registration Form for the I-APS
Table of Contents1997 I-APS Award in Photochemistry
Table of Contents
Table of Contents
Cornelia Bohne, Department of Chemistry, University of Victoria, Canada
and
Matthew B. Zimmt, Department of Chemistry, Brown University, USA
Table of Contents
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104
Table of Contents
Dr. Frank H. Quina, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
Dr. Wyn Jennings - Chemistry Division, NSF, Washington
Prof. Dr. José Galizia Tundisi - President of the CNPq, Brasília
Dr. Gilvan Fernandes Marcilino - Cooperação Internacional, CNPq, Brasília
Sra. Carmem Negraes - Cooperação Internacional, CNPq, Brasília
Ilmo. Sr. Manuel Montenegro - Scientific Attaché, Brazilian Embassy, Washington, DC
Sra. Eliane Silva - Assistant to the Scientific Attaché, Brazilian Embassy, Washington.
Richard A. Caldwell (Univ. of Texas, Dallas), Recent Advances in Photoacoustic Calorimetry.
Daniel E. Falvey (Univ. of Maryland, College Park), Applications of Photothermal Beam Deflection
Calorimetry to Radical Ion Pair Dynamics.
Matthew B. Zimmt (Brown University), Time-Resolved Photothermal Techniques.
Ian R. Gould (Eastman Kodak Co.), Picosecond Transient Absorption and Emission Spectroscopy.
Mohammed S. Farahat (Univ. of Rochester), Transient Absorption Spectroscopy and Exciton Dynamics
in Aggregates of Squaraine Dyes.
Bradley Arnold (Univ. of Maryland, Baltimore Co.), Time-Resolved Linear Dichroism Spectroscopy.
David G. Whitten (Univ. of Rochester), The Complimentary Use of Time-Resolved Fluorescence and
Transient Spectroscopy in Determining Photophysical and Photochemical Paths in Solution and in
Microheterogeneous Media.
Steve E. Webber (Univ. of Texas, Austin), The Use of Fluorescence Polarization and Quenching to
Characterize the Local Environment of Tagged Polymers.
Marcelo Gehlen (Univ. de São Paulo-São Carlos), The Study of Probe-Quencher Mobility in Microheterogeneous
Media by Time-Resolved Emission Techniques.
Frank H. Quina (Univ. de São Paulo), The Use of Time-Resolved Techniques to Investigate Ion Binding at Interfaces.
Ira M. Brinn (Univ. Federal do Rio de Janeiro), Time-Resolved Single Photon Counting - The Kinetics of Excited
State Proton Transfer Systems.
Maria Victoria Encinas (Univ. de Santiago de Chile), Frequency Domain Fluorometric Measurements.
Dirk Nather (Edinburgh Instuments), Multilevel Time-Resolved Single Photon Counting.
Malcolm D. E. Forbes (Univ. of North Carolina, Chapel Hill), Present and Future Directions in Time Domain
Electron Paramagnetic Resonance.
Nancy L. Thompson (Univ. of North Carolina, Chapel Hill), Dynamics of Proteins on Planar Model Membranes:
Measurement by Laser-Based Fluorescence Microscopy.
J. Kerry Thomas (Univ. of Notre Dame), High Energy Excitation of Condensed Systems.
Joel M. Harris (Univ. of Utah), Resolving Intermediates in Multiwavelength Time-Resolved Spectroscopy.
Juan Lopez-Garriga (Univ. of Puerto Rico), Time-Resolved Infrared Spectroscopies: Development and Applications.
Peter C. Ford (Univ. of California, Santa Barbara), Time Resolved Infrared Spectroscopy in Studies of Organometallic Excited States and Reactive Intermediates.
Jeffrey I. Zink (Univ. of California, Los Angeles), Excited State (Time-Resolved) Raman Spectroscopy.
Table of Contents
Summary Report - NSF Workshop on Time-Resolved Techniques in Photochemistry, Photophysics
and Photobiology Session 6 - Time-Resolved Vibrational Spectroscopy
Joel Harris, Department of Chemistry, Univeristy of Utah
Juan Lopez Garriga, Department of Chemistry, University of Puerto Rico
Jeffrey I. Zink, Department of Chemistry, University of California, Los Angeles
| PUMP (timing) | IR PROBE | Detection | |
|
ms-ns (cont monitoring of I vs t) |
CW source - Globar - CO laser - diode laser |
HgCdTe (PV) diode (10 ns risetime) (LN2 cooled) | |
|
ms-ns (transient digitizers) |
- Globar |
STEP-SCAN FTIR with HgCdTe diode | |
|
ps-fs (delay train) |
IR pulse by frequency mixing: ir = 1 -
2- "single frequency" - "broad band" (100 cm-1) |
- IR diodes - up conversion - CCD | |
|
ps-fs (delay train) |
CW IR Diode Laser - "single" frequency |
- up conversion - detect ( probe + ir) |
The field of time-resolved Raman spectroscopy is currently branching into several subfields distinguished by the time scale and hence the physics of the measurements. The oldest and largest branch involves the use of laser pulses and delays that are long compared to the both the period of the molecular vibrations and the vibrational relaxation time. The studies in this branch are thus concerned with vibrationally relaxed species (although the species may be transients in the overall chemical reaction and/or transient excited electronic states). In addition, the standard theories of Raman and resonance Raman spectroscopy are applicable to the interpretation of the spectra of the transient species. A currently developing branch that is reaching a high level of sophistication uses ultra-short (femtosecond) laser pulses. By using ultrashort pulses, the initial vibrational dynamics of a molecule can be observed. The theoretical descriptions of the effects of femtosecond pulses on the molecule are rapidly developing and are different from those that can be used for longer pulses. A third branch uses non-laser methods such as pulse radiolysis or rapid mixing (stopped-flow) to initiate short-lived species of interest, followed by laser Raman detection of the transients.
Time-resolved Raman spectroscopic studies of vibrationally relaxed molecules and intermediates can be divided into two categories, one-color and two-color measurements. In the one-color experiment, both the pump and the probe pulses have the same wavelength. This experiment is the simplest because only one laser is needed. The beam can be split and the probe beam delayed, but usually the experiment is done even more simply by using the leading edge of the pulse as the pump and the trailing edge of the pulse as the probe. In this case, the experimental requirements are drastically simplified; the experimenter irradiates the sample and looks for new Raman peaks at high pulse energies that are not observed in the low pulse energy spectrum where only the Raman peaks from the ground state, intact molecule are observed. This type of experiment can even be done with a CW laser; the time resolution can be provided by the excited state lifetime of the molecule, the lifetimes of the observed photofragments, or by the residence time of the molecule in the laser beam as it is flowed past the beam.
The two-color experiment involves the use of one laser pulse to excite the molecule and a second laser pulse with a wavelength different from that of the first pulse to probe the system. The probe pulse is controllably time-delayed. This experiment requires more complex instruments than the one-color experiment because two different laser sources are required and controlling the time delay of the second pulse requires more effort. The greatest advantage of the two color pump-delay-probe experiment is the flexibility of choosing the pump wavelength to be in resonance with an excited state of the molecule of interest and the ability to choose the probe wavelength to be in resonance with the transient species (to obtain resonantly-enhanced Raman signals) or out of resonance as desired. These considerations are given in Table 2.
Time Scale
1. Laser pulses and delays are long compared to both the period of the molecular vibrations
and the vibrational relaxation time.
- concerned with vibrationally relaxed species (although the species may be transients in the
overall chemical reaction and/or transient excited electronic states).
2.Ultrashort (femtosecond) laser pulses
- initial vibrational dynamics of a molecule can be observed.
- theoretical descriptions of the effects of femtosecond pulses on the molecule are different from those
that can be used for longer pulses.
Methods for Vibrationally Relaxed Molecules
1. One-color Measurements.
- both the pump and the probe pulses have the same wavelength.
- usually the experiment is done by using the leading edge of the pulse as the pump and the trailing edge
of the pulse as the probe
- look for new Raman peaks at high pulse energies that are not observed in the low pulse energy spectrum
- can be done with a CW laser; the time resolution can be provided by the excited state lifetime of the
molecule, the lifetimes of the observed photofragments, or by the residence time of the molecule in the
laser beam as it is flowed past the beam.
2. Two-color Measurements.
- involves the use of one laser pulse to excite the molecule and a second laser pulse with a
wavelength different from that of the first pulse to probe the system.
- probe pulse is controllably time-delayed.
- advantages are the flexibility of choosing the pump wavelength to be in resonance with an
excited state of the molecule of interest and the ability to choose the probe wavelength to be in
resonance with the transient species.
For interpreting Raman spectra where excited state and ground-state bands severely overlap, multidimensional least-squares and factor analysis techniques may be used to resolve the spectra of intermediates in photoreactions. For example, in a one-color Raman experiment, by varying the excitation laser intensity (which drives both the rate of photoexcitation and Raman scattering), Raman spectra of excited states can be resolved by least-squares analysis from scattering by ground states and solvent. Saturation of excited-state populations can also be identified in the dependence of Raman scattering on incident laser energy. By varying the concentration of an excited-state quencher in the sample along with the laser intensity, the Raman spectra of the intermediate sensitizer excited state can be resolved from that of a photoproduct or acceptor excited state. While the one-color instrumentation needed to acquire "fixed-time" kinetic data during the laser pulse is quite simple, the variation of laser intensity or reactant concentration provides a sufficiently informative kinetic modulation of component contributions that their spectra can be unambiguously resolved from the data. These techniques could readily be extended to two-color pump-probe acquisition of transient Raman data where the delay between pump and probe pulses generates a variation in component which would be used to resolve their spectra.
One might speculate briefly on the directions that new technology might take. Several of the techniques noted above allowed for extending the special ranges for TRIR investigations. Although it requires considerable signal averaging (hence would be a problem for photosensitive materials), the relative ease by which the step-scan FTIR instrumentation is automated promises to make this a convenient method for obtaining spectra over broad spectral ranges down to the ns time regime. However, the temporal resolution of step-scan FTIR is certainly limited by the speed and sensitivities of the detectors used and intensities of the black body probe sources. For the ultrafast systems, the up conversion of a broad band IR source allows the recording of range of IR frequencies to be recorded with highly sensitive visible range CCD detectors. It would be especially attractive if such a broad band IR source could be recorded directly with an IR diode array device or other multichannel detector. It seems that an attractive direction for future development in the area of TRIR detectors would be to exploit the known technology of infrared imaging used in IR cameras for military and civilian applications.
In the case of transient Raman spectroscopy, the technology to generate and measure transients on time scales as short as the femtosecond regime now exists. The challenges lie in the theoretical interpretations of the spectra. For picoseconds or longer, the challenges lie in developing applications.
Table of Contents
Time Resolved (CW) Electron Paramagnetic Resonance Spectroscopy
Malcolm D. E. Forbes, Department of Chemistry, University of North Carolina at Chapel Hill
While it lacks the sensitivity of conventional continuous wave (CW) steady-state electron paramagnetic resonance (EPR) spectroscopy, the time resolved (CW) EPR method (TREPR) has several clear advantages in cost, spectral resolution and ease of data acquisition over pulsed transient EPR methods such as Fourier Transform (FT) EPR and Electron Spin Echo Envelope Modulation (ESEEM). The development of higher frequency TREPR at Q-band (35 GHz) in the author's laboratory has provided a time response on the order of 25 ns which is laser pulse width and jitter-limited. This spectrometer could conceivably reach a time response of 5 ns with a suitable excitation source, which is inherently limited by the microwave cavity quality factor Q. This time response is comparable to that of nanosecond flash photolysis/transient absorption spectroscopy. Increased spectral resolution, the effects of g-factor differences on chemically induced electron spin polarization (CIDEP) mechanisms, longer spin relaxation times, and the ability to observe magnetic field effects on individual spin states are all motivations for performing this experiment at Q-band and higher frequencies. The standard commercially available frequency of X-band (9.5 GHz) is still extremely useful for many studies and is especially useful to us in comparison to Q-band for magnetic field effects on individual spin states.
Research groups carrying out this experiment have applied it to many problems in organic photochemistry and in studies of molecular structure of organic reactive intermediates. In our group we have specialized in multiple-frequency TREPR of biradicals, electron transfer reactions and polymer photodegradation. Spin exchange interactions in flexible biradicals have been studied as function of structure, solvent and temperature. The primary photodegradation events in solutions of alternating alkyl-CO copolymers has been observed in real time, and the spin multiplicity of the excited states involved in electron transfer from tetramethylphenylenediamine to various quenchers have been conclusively assigned. A breaking development from our laboratory is the observation of major solvent effects on spin exchange couplings in liquid and supercritical carbon dioxide.
Future directions in this field are centered around several instrumentation advances that are anticipated within the next two years. The most important of these is the construction of a tunable, time-resolved EPR spectrometer at the National High Magnetic Field Laboratory in Tallahassee, Florida, which will cover a frequency range of 110 to 440 GHz. The time response of this instrument is expected to be on the order of 200-300 picoseconds. A 700 GHz spectrometer is expected to be online at this laboratory in the early part of the next decade. Cryogenically-cooled microwave bridges that have significantly lower thermal noise are also under construction in Gareth Eaton's laboratory in Denver. The construction of loop-gap resonators for high sensitivity in aqueous samples is a major thrust for biomedical EPR applications, and the National Biomedical EPR Centers at the University of Illinois and the Medical College of Wisconsin are active in this area. Jack Freed's lab at Cornell is developing exciting 2-D EPR experiments for studies of dynamics in solution. Perhaps the biggest step forward in future EPR technology will come when fast-switching diodes become available that allow very sharp, short microwave pulses which will allow uniform high power excitation of the entire spectral width of a typical organic radical. The FT-EPR technique will then become as ubiquitous as FT-NMR.
In our laboratory, we continue to synthesize novel precursors to radical pairs and biradicals that help us learn about spin polarization mechanisms such as the radical pair mechanism (RPM), the spin correlated radical pair (SCRP) mechanism, and the triplet mechanism (TM). All three of these mechanisms depend greatly on the medium, which has allowed us to investigate solvent polarity, viscosity, and confinement effects on all of them. We also continue to work with non-traditional sample geometries such as high pressures (up to 2000 psi in liquid carbon dioxide), slurries (for surface/solvent interface studies), and thin films for polymer photodegradation reactions. The modern approach to sample geometry and positioning problems is the independent construction of microwave resonators appropriate for the given geometry, rather than try to reduce the size or otherwise alter the sample for tunability with commercially available resonators. The move to higher frequencies will require even more innovation in this area as sample size and dielectric constant become even more critical issues. The improved signal-to-noise ratios, better spectral resolution, and faster time response expected at higher frequencies make these developments very promising for the future of time-resolved EPR. The field is still young!
Upcoming Meetings
Please send new meeting announcements to: Kirk Schanze or
Willie Leigh.
Summary Report - NSF Workshop on Time-Resolved Techniques in Photochemistry, Photophysics and
Photobiology Session 5 - Special Time Resolved Techniques Part A.
Table of Contents
Table of Contents