bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction Dynamics of Electronically Excited Calcium Atom
Authors: Verdasco E. , Menéndez M. , Garay M. , Ureña A. González , D′azy O. Benoist , Poblete F. J. , Taïeb G.
Published: March 2007

Absolute values of the total chemiluminescence cross‐section for the beam‐gas Ca(3P, 1D) + Cl4C → CaCl(A, B) + Cl3C and Ca(3P, 1D) + SF6 → CaF(A, B) + SF5 reactions have been measured at low collision energy, ET = 0.15 and 0.14eV, respectively. Both metastable atomic calcium states Ca(3P, 1D) were produced under low voltage dc‐discharge conditions. By changing the discharge conditions, different metastable concentrations were produced to measure the state‐to‐state cross‐section for both 3P and 1D reactions. The following values for the total chemiluminescence cross‐sections were obtained:

σ = 1.77 Å and σ = 0.25 Å for the Ca(3P, 1D) + Cl4C → CaCl(A, B) + Cl3C reaction.

σ = 0.59 Å2 and σ = 0.56 Å2 for the Ca(3P, 1D) + SF6 → CaF(A) + SF5 reaction.

σ = 0.04 Å2 and σ = 0.12 Å for the Ca(3P, 1D) + SF6 → CaF(B) + SF5 reaction.

In addition, beam‐beam experiments were carried out at the same average low collision energy that of the beam‐gas, and therefore, normalization between both experiments was possible. This procedure allowed us to obtain the excitation function of the Ca(1D) + SF6 reaction in absolute values over the 0.15–0.60eV collision energy range.

On the other hand, by simulation, the ratio of CaCl(B‐X/A‐X) emissions intensities was found to be of 0.15. The variation of this ratio with the relative concentration of 1D/3P in a Broida oven leads to the conclusion that this state favours the formation of the B state in the chemiluminescent Ca(3P, 1D) + CH3CHCl2 → CaCl(A, B) + CH3CHCl reaction.
A New Technique for Ultrafast Velocity Distribution Measurements of Atomic Species by Post‐Ionization Laser Induced Fluorescence (PILIF)
Authors: Tabares F. L.
Published: March 2007

A new method for single shot velocity distribution measurement of metallic impurities of relevance for studies involving continuous sources, such as limiter experiments in fusion devises or sputtering experiments, based in the combination of Resonant Enhanced Multiphoton Ionization (REMPI) and Laser Induced Fluorescence (LIF) is proposed. High ionization yield and good time resolution are expected according to the numerical simulation of the experiment that has been run for several atomic species. Other possible applications of REMPI to plasma edge physics and to conventional techniques for velocity distribution measurements are briefly addressed.
Chemical Intensification of Nonlinear Multi‐Wave Interactions
Authors: Galushkin M. G. , Gordon E. B. , Drozdov M. S. , Sviridov K. A.
Published: March 2007

Nonlinear interaction of laser emission with a chemically reactive medium, in which a branched chain reaction may readily occur, has been analyzed aiming at essential intensification the contrast of photochemically induced phase gratings. For the model system CS2/O2, the degenerated four‐wave mixing is theoretically studied under the assumption of CS2 photodissociation followed by subsequent secondary reactions induced by reactive photodissociation products. For varied CS2 concentrations and incident flux intensities, the dynamics of nonlinear reflection has been analyzed and same laser applications of such systems are suggested.
UV Laser Decay of Oxygen‐Deficient Centers in Silica Glasses
Authors: Bagratashvili V. N. , Tsypina S. I. , Alimpiev S. S. , Simanovski Ya. O. , Prokhorov A. M. , Rybaltovski A. O.
Published: March 2007

Oxygen‐deficient centers decay with simultaneous formation of color centers in IR and UV grade silica glasses under KrF laser irradiation was studied. The nonexponential dependence of the ODC photodecay in silica glass on the UV irradiation dose (number of laser pulses) was observed. Postpulse long‐time temporal behaviour of recombination luminescence and laser induced photoconductivity was analyzed for the two types of glasses in time scale up to 0.5 ms. Long time fluorescence tail is attributed to migration of electrons through the shallow traps before recombination and recovery of ODC. The models of postpulse recombination which can explain the observed nonexponential behaviour of ODC decay (geminal and homogeneous) are discussed. The principle part of impurities caused electron traps in the postpulse ODC recombination is shown.
Formation and Luminescence of Molybdenum Atoms After UV Multiphoton Excitation of Gas Phase Mo(CO)6
Authors: Belyayev Yu. E. , Dem′yanenko A. V. , Puretzky A. A.
Published: March 2007

The delayed luminescence of Mo atoms was observed in XeCl laser excitation of Mo(CO)6 gas. The observed luminescence was explained by production of Mo Rydberg atoms under UV laser excitation of Mo(CO)6.
New Directions in Multiphoton Dissociation
Authors: González-Díaz P. F. , Santos M. , Sigüenza C. L. , Torresano J. A.
Published: March 2007

Unimolecular multiphoton dissociation offers us a rather complete scheme where the transition from quantum mechanics to the classical regime can be experimentally followed. In the light of this idea, a new interpretation of the unimolecular multiphoton dissociation process is presented. The role that the intramolecular generation of instabilities and chaos may play in that process is discussed, both in single and double exposure experiments. Delayed double irradiation is also discussed and a criterion to define an effective single pulse notion in that kind of experiment is given.
Chemical Lasers From the Photodissociation of Nitrosyl Halides
Authors: Barrero J. I. Del Barrio , G.-Tablas F. M.
Published: March 2007

New NO laser emission from the photodissociation of BrNO has been observed between vib‐rotational levels of the ground state of NO, using He and Br2 as buffer gases. Also, from the ClNO photodissociation several new NO vibro‐rotational lines have been observed.

The presence of a buffer gas was necessary to observe laser emission from BrNO and ClNO.

The temporal behavior of the NO laser emission from the photodissociation of both nitrosyl halides has been studied.
Laser‐Induced Charge Transfer Under Crossed‐Beam Conditions: Application to the Na + I2 → Na + + I2− System
Authors: Bañares L. , Skowronek S. , Perdiguero C. , Ureña A. González
Published: March 2007

A crossed‐beam charge transfer study was carried out for the Na(32P3/2,1/2) + I2 → Na+ + system using laser excitation of the Na atom. The excitation functions were measured for the title reaction, searching for spin orbit effects. A common energy threshold of E0≃0.23eV was found for both processes. In addition, similar post‐threshold laws for each spin‐orbit state indicate the absence of such effects over the low collision energy range.
Direct Measurements of Removal Rates of CHF(X˜1A′(0,1,0)) by Simple Alkenes
Authors: Fernández José A. , de Zárate Alfredo Ortiz , Rayo María N. Sánchez , Castaño Fernando
Published: March 2007

Direct measurements of the rate constants for collisional removal of CHF by argon (Ar), ethylene (C2H4), propene (C3H6), 1‐butene (1‐C4H8), iso‐butene (i‐C4H8), 1,3‐butadiene (C4H6), are reported. CHF was prepared by IRMPD of precursor CH2F2. Fluence independence removal rate constants by Ar, ethylene and propene are: 0.0045, 2.70 and 2.46 × 10−11 cm3 molecule−1 s−1, faster than the rates for the vibrational ground state. 1,3‐butadiene was measured at a fluence of 42Jcm−2, yielding a value of 0.81 × 10−11 cm3 molecule−1 s−1. Iso‐butene has fluence dependence removal rates, given 1.28 and 0.92 × 10−11 cm3 molecule−1 s−1 for fluences of 50 and 32Jcm−2 respectively. For 1‐butene a non‐linear Stern‐Volmer behaviour has been observed and attributed to fast resonant vibrational‐to‐vibrational (V‐to‐V) intermolecular energy transfer. The influence of this (V‐to‐V) energy transfer on the removal rates is discussed.
Spectroscopic Sensor as a Mineral Oil Indicator
Authors: Viñas M. Hernández , Escudero J. L. , Campillo A. López , Murciano E. Martínez , Montoro T.
Published: March 2007

In this work a spectroscopic method to measure the degradation degree of paraffinic mineral oils is proposed. The behaviour of some molecules (indoles) in solution versus their surrounding environment (solvent polarity and viscosity) is the basis of the method. Experimental results obtained for VESTAN oil, confirming this theoretical scheme, are presented.
Dynamics of the B 3Π(0u+) and A 3Π(1u) States of Chlorine by Laser Induced Fluorescence
Authors: Martínez E. , Basterrechea F. J. , Cabañas B. , Puyuelo P. , López M. R.
Published: March 2007

Chlorine B 3Π() state lifetimes have been measured by laser‐induced fluorescence in several predissociated (υ′ = 14–19,21) and non‐predissociated (υ′ = 5–12) levels. Trial and error Franck‐Condon calculations have been performed to check the nature and position of the predissociating state. The results have been used to give a value of Re for the A 3Π(1u) state responsible for predissociation, Re = 2.48 ± 0.01 Å. The obtained data show that interference effects due to crossing between B and A states modify the lifetimes of the B state appreciably. The inadequacy of the low‐lying vibrational levels region, i.e. υ′ < 8, to measure the radiative lifetime of the B state (τR(B)) is shown. Previous values for τR(B) can therefore be affected by considerable errors.
From Selective to Non‐Selective Vibrational Predissociation in Glyoxal van der Waals Complexes
Authors: Halberstadt N. , Soep B.
Published: March 2007

Vibrational predissociation (VP) of glyoxal complexes formed in a supersonic
expansion, has been studied in several vibrational levels of the first excited singlet
electronic state S1( 1Au) of glyoxal. Light complexes as H2‐glyoxal display a nice state
to state dissociation. Whereas the analysis of the fluorescence spectrum, together with
lifetime measurements, have shown that VP is in competition with other intramolecular
vibrational energy redistribution processes in these systems, as well as inter‐system
crossing (ISC). Glyoxal‐Ar and glyoxal‐Kr behave very similarly. In particular, two
isomers exist with different dissociation schemes (but similar for the same isomer of
Ar or Kr‐complex), and Kr does not seem to enhance ISC. Thus selectivity in the
dissociation routes has to be understood as a competition between these deactivation
channels.
Low Energy Modes of the Hydrogen‐Bonded Dimer of Benzoic Acid
Authors: Poeltl David E. , McVey Jeffrey K.
Published: March 2007

Hydrogen bonding in isolated, cooled dimers of benzoic acid is explored following
preparation in a free jet expansion. Analysis of the laser excitation spectrum in the
low energy region allows for the identification of the modes involved in hydrogen
bonding in the excited state of the dimer, and cluster formation is noted between the
ground state dimers. Van der Waals complexes of the dimer with rare gas atoms are
also identified. Assignments of the observed dimer modes have been made and the
results are compared with previous studies in solution and matrices and with normal
mode analyses.
Statistical Theory of Unimolecular Reactions and Intramolecular Dynamics
Authors: Marcus R. A.
Published: March 2007

In the present lecture we review experimental and theoretical developments in the
field of intramolecular dynamics during the past sixty years. In a concluding section
we consider possible implications for intramolecular laser selective chemistry.
Laser Spectroscopy of Solids
Authors: Brewer Richard G. , DeVoe Ralph G.
Published: March 2007

Remarkably narrow optical homogeneous linewidths of the order of 1 kHz have now
been observed in low temperature zero‐phonon transitions of dilute impurity ion
crystals, such as Pr3+ in LaF3. Novel nonlinear optical resonance techniques have been
devised for this purpose using ultrastable phase locked cw dye lasers where the
measurements are performed either in the frequency domain (hole burning) or in the
time domain (coherent optical transients). These studies effectively bring the Mossbauer
effect into the optical region. Hence, the observed linewidths are no longer limited by
inhomogeneous strain broadening (∼5 GHz) or even by static local fields due to
neighboring spins (∼100 kHz). However, weak magnetic field fluctuations from local
spins are readily detected. As an example, spin decoupling and line narrowing, which
are well known in NMR, are observed in an optical transition of Pr3+:LaF3 at 2 K
where the  19F– 19F dipolar interaction is quenched and the optical linewidth drops
from 10 to 2 kHz, clearly demonstrating the spin broadening mechanism. Results will
be discussed in terms of a Monte Carlo line broadening theory.
The Spectroscopy of Transition States in H+H2 Reaction, and NaI Photodissociation
Authors: Foth H.-J. , Mayne H. R. , Poirier R. A. , Polanyi J. C. , Telle H. H.
Published: March 2007

(a). We have computed an approximate absorption spectrum for unstable intermediates
which constitute the transition states in the fundamental exchange reaction . Reaction takes place across the Siegbahn, Liu, Truhlar, Horowitz
(SLTH) ground state energy surface, and electronic excitation is to the bound state
that correlates with H*(22P)+H2. Features in the spectrum are indicative of the
favored turning points for the mean of many classical trajectories across the SLTH
surface. (b). Preliminary experimental data are reported which give evidence of emission
arising from the transition states of NaI≠* in the (cw or pulsed) photolysis of
≠*→Na*(32P)+I.
The observed transition state emission is compared with a simple calculation.
On the Question of Mode‐Specificity in Unimolecular Reaction Dynamics
Authors: Miller William H.
Published: March 2007

Unimolecular decomposition following state‐specific laser excitation is considered. If
the transition state for the unimolecular reaction possesses any geometrical symmetry,
then it is shown that this can lead to mode‐specificity in the decay rates (i.e., different
states with essentially the same total energy and angular momentum react at significantly
different rates). This is illustrated for a model problem of two coupled oscillators (the
Henon–Heiles potential) and also for the unimolecular dissociation of formaldehyde,
H2CO→H2+CO, which has a planar transition state. Dynamical calculations indicate
that there may also be a significant degree of mode‐specificity for the formaldehyde
reaction beyond that due to symmetry.
Local Mode Excitation for Time Resolved Unimolecular Decay Studies
Authors: Rizzo T. R. , Cannon B. D. , McGinley E. S. , Crim F. F.
Published: March 2007

Laser excitation of overtone vibrations is a useful technique for selectively preparing
molecules for state‐selected unimolecular reaction studies. In addition, these studies
provide new data on overtone vibration transitions in the excited molecules. Data
obtained from state‐selected unimolecular decay experiments and photoacoustic
measurements provide local mode parameters for overtone vibrations in tetramethyldioxetane,
t‐butylalcohol, t‐butylhydroperoxide, and hydrogen peroxide.
Phase Coherence in Multiple Pulse Optical Spectroscopy
Authors: Warren Warren S. , Zewail Ahmed H.
Published: March 2007

In this paper we describe a new technique for the generation of multiple pulse phase
coherent sequences in optical spectroscopy. The technique is an extension of the
acousto‐optic modulation and fluorescence detection methods developed for optical
transitions by Zewail and Orlowski (Zewail et al., Chem. Phys. Lett.48, 256 (1977);
Orlowski et al., Chem. Phys. Lett.54, 197 (1978)). Application of these multiple pulse
trains (of different phases) to optical transitions of two‐level and multilevel systems is
demonstrated experimentally. It is shown that they can be used to (i) suppress spontaneous
emission background, (ii) enhance coherent transients such as photon echoes,
(iii) measure additional relaxation parameters in systems with complex rotational‐vibrational
levels, and (iv) enhance the effective laser bandwidths through composite
pulse trains, as demonstrated on I2 gas. Finally, the potential of this development is
extended to the possibility of observing selective multiquantum excitation in molecules.
Picosecond Laser Chemistry in Supersonic Jet Beams
Authors: Zewail Ahmed H.
Published: March 2007

In this review we describe the development and the applications of the picosecond‐jet
technique, which utilizes a picosecond laser and a supersonically‐cold jet beam of large
molecules. The applications include studies of coherence (quantum beats), photodissociation,
isomerization, and partial solvation. The results emphasize the role of
intramolecular energy redistribution, and provide evidence for intramolecular threshold effect
for rates vs. excess molecular energy. Simple theory for this redistribution of
energy among certain modes in molecules is given, and comparison with RRKM
calculation is also made to assess the nature of the statistical behavior for the redistribution.
Picosecond Processes in Chemical Systems: Vibrational Relaxation
Authors: Heilweil E. J. , Moore R. , Rothenberger G. , Velsko S. , Hochstrasser R. M.
Published: March 2007

A review is presented of our recent studies of vibrational energy relaxation of moderately
sized molecules in a variety of media and of the effect of vibrational relaxation on
processes such as molecular rearrangements.

Data are presented on intramolecular dynamical processes involving p‐difluorobenzene
and an experiment is described which allows the study of spectral evolution on the
picosecond timescale under collision‐free conditions.

The vibrational (T1) relaxation of the apparently simple system consisting of a
diatomic CN− ion in aqueous solution was studied and found to be in the range of a few
picoseconds and to be concentration dependent. These results, and the effects of
counterions, are suggested to be the result of aggregation of the ions. A discussion of
the Raman lineshapes is given in relation to the measured T1 times.
Intermolecular and Intramolecular Excited State Charge Transfer
Authors: Eisenthal Kenneth B.
Published: March 2007

A primary mechanism of energy relaxation and chemical change in
organic molecules in excited electronic states is charge transfer. 1 The
charge transfer process can be intermolecular, involving an excited
molecule and a neighboring molecule, one serving as an acceptor and
the other as a donor molecule, or intramolecular, involving a charge
redistribution in the excited molecule which produces a very large
excited state dipole moment.

In our investigations of the dynamics of these various charge transfer
processes, a picosecond laser pulse was used to excite the molecules
of interest. The charge transfer dynamics were monitored by a variety
of techniques, including transient absorption of the excited charge
transfer complex (exciplex) or ion radicals by a time delayed
picosecond pulse, and fluorescence from the exciplex and from the
initially excited molecule using a picosecond streak camera for
detection.
Application of Photoacoustic Calorimetry to the Photofragmentation of Cr(CO)6
Authors: Simon John D. , Bernstein Mark , Peters Kevin S.
Published: March 2007

Photolysis of Cr(CO)6 in cyclohexane yields solvated pentacarbonyl species within
25 ps. Using high‐speed photoacoustic calorimetry, we have determined the heat of
reaction for this photofragmentation, directly measuring the energy required to break
a single metal–carbonyl bond followed by solvation of the fragments. The energy
required to photochemically dissociate a single CO in cyclohexane exceeds the gas
phase average bond dissociation energy by at least 11 kcal/mol. However, the determined
heat of reaction agrees well with the activation energies derived from thermal
decomposition kinetics.
Molecular Dynamics of Chemical Reactions in Solution
Authors: Bado Philippe , Berens Peter H. , Bergsma John P. , Coladonato Mark H. , Dupuy Charles G. , Edelsten Pamela M. , Kahn Jason D. , Wilson Kent R. , Fredkin Donald R.
Published: March 2007

We hope to answer one of the most fundamental and important unsolved questions
in chemistry: how, from a molecular perspective, do chemical reactions in solution
actually occur. The key to solving this long‐standing problem is to understand the
molecular dynamics, i.e., the motions of the atoms and the forces that drive them. We
have already developed theoretical techniques and computational procedures involving
specialized computer hardware needed to calculate the molecular dynamics for many
chemical reactions in solution. From the dynamics we have derived the interface for
experimental verification, namely transient electronic, infrared, and Raman spectra as
well as X‐ray diffraction, all of which are potentially observable manifestations of the
atomic motions during the reaction. We have tested our approach on the simple
inorganic I2 photodissociation and solvent caging reaction. The agreement between
molecular dynamics based theory and experimental picosecond transient electronic
absorption spectrum as a function of solvent, time, and wavelength is sufficiently close
as to indicate that for the first time we are discovering at least part of the molecular
dynamics by which a real solution chemical reaction takes place.
Studies of Molecular Adsorbates at Interfaces by Optical Second‐Harmonic Generation
Authors: Tom H. W. K. , Heinz T. F. , Shen Y. R.
Published: March 2007

Optical second‐harmonic generation (SHG) is surface‐specific and has the sensitivity
to detect submonolayers of molecules. It can be applied to study molecular adsorbates
at the interface between any two centrosymmetric media. This has been demonstrated
by using dye and p‐nitrobenzoic acid (PNBA) molecules adsorbed on smooth fused
quartz substrates as examples. With resonant SHG, the S0 →
S2 transition of the
adsorbed dye molecules was measured. From the polarization dependence of the SHG,
the orientation of PNBA at both the air/quartz and the ethanol/quartz interfaces was
deduced. By varying the concentration of PNBA in ethanol, an adsorption isotherm
for PNBA at the ethanol/quartz interfaces was also obtained.
Multiphoton Mass Spectrometry: Metastables
Authors: Kühlewind H. , Boesl U. , Weinkauf R. , Neusser H. J. , Schlag E. W.
Published: March 2007

Multiphoton absorption in molecules is a facile method of producing ions. This
technique enables one to use visible or near ultraviolet light for the production of
molecular ions. This ionization is shown to proceed with near 100% efficiency in a
well localized source, the focus of the laser, and a well defined time, the excitation
pulse length of the laser. This makes for an ideal ion source for a mass spectrometer.
A time‐of‐flight configuration will be discussed with a present mass resolution of
3000–4000. This high transmission TOF enables a complete analysis of all ions from
a single laser shot, providing suitable electronics is available. This unit can also be
used to obtain new information on the behavior of ion decay processes near their
energetic thresholds (metastables). The method provides detailed information when
the laser wavelength or its intensity is tuned. Comparison to conventional mass
spectrometry will be given.
A Dye Laser Pumped by an Air Laser
Authors: El-Raey M. , Helmi M. S.
Published: March 2007

A modified dye laser system operating at UNARC is discussed. The dye laser (peak
wavelength ≈ 440 nm) is pumped by an air/N2‐laser. The dye is a new one, Tinopal,
provided by CIBA Co. in Egypt. The dye laser/air laser characteristics are presented.
Time‐Resolved Resonance Raman Spectroscopy of Excited Triplet State All-Trans‐Retinal: Excitation Profiles, Intersystem Crossing Kinetics, and O2 Quenching
Authors: Atkinson G. H. , Pallix J. B.
Published: March 2007

The time‐resolved resonance Raman (TR3) spectra of excited triplet state all-trans‐retinal
(ATR (T1)) are analyzed with respect to (1) time‐resolved excitation profiles
(TREP), (2) T1 → S0
intersystem crossing rates, and (3) O2 quenching kinetics. These
TR3 data are used to comment on the electronic characteristics and kinetic decay of
the excited triplet state of a specific retinal isomer in room temperature solutions.
Photophysical Processes in Simple Molecules Excited by Synchrotron Radiation
Authors: Nenner Irène
Published: March 2007

The elementary photophysical processes following the absorption of a VUV photon
(above 10 eV) by an isolated molecule are described. Special emphasis is made on
photoionization and photodissociation processes, on the basis of recent results obtained
by different experimental methods associated to synchrotron radiation. Discussion is
made within the frame of recent theories. Future trends are also mentioned in connection
with new synchrotron sources. NaINaI≠*→Na*(32P)+I.
Multiphoton Ionization Mass Spectrometric Studies of Transition Metal Carbonyl Complexes
Authors: Leopold D. G. , Vaida V.
Published: March 2007

The multiphoton photochemistries of a variety of gas phase transition metal carbonyl
complexes are investigated by MPI time‐of‐flight mass spectrometry, and results
indicate that molecular fragment ionization can compete with atomization in these
systems. Molecular ions detected include a variety of homonuclear and heteronuclear
bare metal clusters, metal‐sulfur clusters and metal monocarbonyls. Thus, multiphoton
excitation of stable metal carbonyl compounds provides a versatile synthetic route to
highly unsaturated neutral and ionic gas phase clusters which offers unique product
cluster specificity and does not require the use of high temperature sources. The
detection under collision‐free conditions of bare metal dimers and trimers following
MPI of several dinuclear and trinuclear metal cluster carbonyl compounds, respectively,
indicates that dissociative CO loss can compete with metal–metal bond cleavage as a
primary excited state reaction upon UV photolysis of these systems.
Electronic Energy Partitioning in Photodissociation
Authors: Singer Sherwin J. , Freed Karl F. , Band Yehuda B.
Published: March 2007

Despite the apparent simplicity of photodissociation in diatomic molecules, some of
the essential physics of this process is not understood when there is fine structure in
the atomic photofragments. Previous theories cannot treat the branching ratios and
angular distributions of the individual fine structure sublevels. We have developed a
complete quantum mechanical theory of the effects of nonadiabatic couplings and of
electronic angular momentum on the fine structure branching ratios, angular distributions,
and polarization in diatomic photodissociation. When the photofragments separate
with large relative kinetic energy, simple limiting expressions can be obtained for
branching ratios and the symmetry parameters which characterize fragment angular
distributions and polarized fluorescence from excited fragments. Information about
the symmetry of the molecular states involved in the optical transition which dissociates
the molecule may be deduced from fine structure branching ratios and asymmetry
parameters in the high energy limit. At low relative kinetic energies where non‐adiabatic
couplings are crucial, cross sections and asymmetry parameters exhibit interesting
behavior which intimately reflect the shape of the dissociative molecular surfaces. We
employ the example of sodium hydride photodissociation to produce  2P excited sodium
atoms as a model system because of the availability of ab initio potential curves and
oscillator strength matrix elements. The low energy photodissociation cross section
and angular distributions are shown to exhibit resonances which arise in part due to
non‐adiabatic spin–orbitand Coriolis couplings. Their energy dependence can therefore
be utilized to probe the nature of potential curves which are not directly pumped in
optical absorption processes and may therefore provide a unique spectroscopic means
for measuring properties of these “dark” states.
Theory of Dissociative Ionization Processes
Authors: Kanfer S. , Shapiro M.
Published: March 2007

A quantum mechanical theory for the ℏω + AB → A + B+ + e− three body breakup is
presented. The theory is based on the Continuum Coupled Channels expansion (CCC)
in which the three body wave‐function is expanded in terms of square integrable and
(flux carrying) continuum states. The theory consistently treats the accompanying
processes of three body inelastic collisions, dissociative attachment and Penning ionization.
Applications to the dissociative photoionization of H2 and HD are presented.
The relevant equations are solved exactly using the Artificial Channel method. Excellent
agreement is obtained with experiment, concerning the proton kinetic energy
distribution.
On the Extraction of Time Information From Energy‐Resolved Experiments
Authors: Durup Jean
Published: March 2007

It is well known that in principle energy‐resolved and time‐resolved experiments
provide complementary information. A few examples are reviewed where the time
evolution of rapidly relaxing molecular systems is or could be better studied by
energy‐resolved experiments: (1) the evolution of a pair of resonances coupled with
each other through a set of continua, (2) an irreversible relaxation of the intermediate
state in the two‐photon excitation of a polyatomic molecule, and (3) the derivation of
a “dissociation time” from the angular distribution of fragments from photodissociation
by linearly polarized light. In the first case it is shown how all parameters necessary
for a time‐dependent description may be obtained from the measurement, as functions
of the excitation wavelength, of both the total absorption cross section across the
resonances and the partial cross section for a single exit channel. In the last two
cases the relevance of a description in terms of an “eigentime” of the molecule is
demonstrated.
Reduction of the Pathways of Photochemical Gasphase ReactionsInduced by Multiple Photon IR Laser Excitation of Molecules
Authors: Bagratashvili V. N. , Kuzmin M. V. , Letokhov V. S.
Published: March 2007

Two different cases, (1) thermal initiation and (2) collisionless IR multiple photon
(MP) initiation, of initiating the model reaction of the successive decay of polyatomic
molecules ABC → AB + C,AB → A + B are considered for the case when the intermediate
product AB is desired. In the case when the desired product AB is thermally less
stable than the original one ABC the high output of AB under the thermal initiation
is impossible. However by means of IR MP initiation one can obtain a high yield of
the desired product, i.e., nearly 100%. The reduction of the chemical reaction pathways
takes place for the IR MP initiation. This is due to the extreme intermolecular
nonequilibrium achieved under IR MP initiation of the reaction. Unlike the thermal
initiation when all the reaction products are of equally high temperature, under IR
MP initiation the temperature of the intermediate product TAB is lower than that of
the original one TABC and a further decay of the AB species does not occur.
Structure and Properties of the Triplet State of StyreneDerivatives Studied by Laser‐Flash‐Photolysis
Authors: Bonneau R. , Herran B.
Published: March 2007

The triplet state of a series of compounds, each containing the styrene moiety, has
been studied by nanosecond laser flash photolysis. The lifetimes, the TT absorption
spectra and the rate constants for deactivation by several quenchers have been determined.
It is shown from these results that, in the triplet state of styrene derivatives in
their lowest energy conformation, the double bond is twisted by 90° for flexible
molecules (perpendicular triplet) or by an angle as large as allowed by the molecular
framework of rigid molecules (twisted triplet). There is no equilibrium between planar
and perpendicular (or twisted) triplets, in contrast with the case of stilbene. The
influence of substituants on the lifetime of the perpendicular triplet and the mechanism
of quenching of this species by oxygen have been investigated.
Time‐dependent Picosecond Transient Absorption Spectra of9‐Acetylanthracene, Benzophenone and Acridine in Solution
Authors: Hamanoue Kumao , Nakajima Kazuo , Hidaka Toshiharu , Nakayama Toshihiro , Teranishi Hiroshi
Published: March 2007

The transient absorption spectra of the title compounds in solutions at room temperature
have been measured on the picosecond time scale. For 9‐acetylanthracene and acridine
there were measurable changes of the spectral shapes in the first picosecond region,
while no spectral change was observed for benzophenone.
Fluorescence Quantum Yield and Free Rotor Effect
Authors: Abdel-Mottaleb M. S. A.
Published: March 2007

It was found that the weakly fluorescent trans‐2(4′‐N,N‐dimethylaminostyryl)‐
pyridinium betaine dyestuff (1) becomes efficiently fluorescent in very viscous media.
The fluorescence quantum yield (φF) for dyestuff (1) approaches unity in ethanol–ether
(1: 1) glass at 98 K. Moreover, the fluorescence wave‐length is blue shifted (1874 cm−1)
when the temperature is lowered to 98 K. The results are rationalized as being due to
solvent viscosity dependent rate constant for a radiationless internal conversion process,
involving rotation of the different parts of the molecule, a free rotor effect. The rate
of internal rotation was estimated to be 3.4 × 1011 s−1. The results suggest that this
molecule can be used as a fluorescent probe to study microscopic structural changes in
surrounding media occurring on the picosecond time scale.
Neutral and Ionic ParticleEmission Produced by LaserIrradiation of a GaAs Surface
Authors: Möhlmann G. R.
Published: March 2007

The emission of gas phase particles from a GaAs surface, due to irradiation at 1064 nm
by an unfocussed Q‐switched Nd:YAG laser beam, has been studied. Mass spectra
have been recorded with the aid of a quadrupole mass spectrometer, and the ion‐neutral
ratio of the emitted particles has been measured with an electrical diode set up. The
applied incident laser radiation power density was varied in the range 1.2–9.6 × 107
Watts/cm2 and was delivered as 10 ns (fwhm) long pulses. It appeared that mainly Ga
atoms and As2 molecules were emitted, together with minor amounts (<1%) of Ga2
and GaAs molecules. Besides the emission of neutral particles, the formation of Ga+
atomic ions was observed. By measuring the ratio of Ga+ ions and Ga neutral atoms
it could be shown that the (ionic) particle emission is governed by a thermal mechanism
for 1064 nm incident radiation. This latter experimental result differs from that obtained
if a ruby laser (694 nm) is used as the radiation source.
Measurements of the Relaxation Kinetics of Photo‐Excited Enol Form of Dibenzoylmethane
Authors: Yankov P. D. , Saltiel S. M. , Tomov I. V. , Markov P. J. , Petkov I. K.
Published: March 2007

The decay rate of the excited state of the enol form of dibenzoylmethane (DBM) in
different solvents is measured directly using nanosecond light pulses. The observed
relaxation kinetics is explained by the formation of three intermediate forms of the
excited cis‐enol form of DBM. The decay rates of the intermediates and their absorption
cross sections for λ = 266 nm are reported too.
Direct Determination ofAluminium Concentration inHuman Blood Through LaserPhotoionization Spectroscopy
Authors: Bekov G. I. , Letokhov V. S. , Radayev V. N.
Published: March 2007

The results of aluminium content measurements in human blood by the method of
laser stepwise photoionization of atoms in combination with vacuum thermal atomization
of organic substance are presented. The analytical procedure was as follows. Dry
blood residium obtained after drying of 40 μl natural blood was stepwise heated in
vacuum to 1800℃. The aluminium atoms produced in an atomic‐molecular beam were
excited to a Rydberg state in two steps by laser radiation and then efficiently ionized
by electric field pulse. The resulting ions were detected with an electron multiplier.
The calibration curve obtained for aqueous solutions of AlCl3 was used for quantitative
determination of aluminium content. The measured value of aluminium concentration
in human blood came to (230 ± 50) ng/ml.
Classical Trajectory Calculationsof Infrared MultiphotonAbsorption and Dissociation
Authors: Gray S. K. , Stine J. R. , Noid D. W.
Published: March 2007

A review of classical trajectory calculations of infrared multiphoton absorption and
dissociation is presented. These calculations have demonstrated that the classical method
can be useful for interpreting experimental results and for understanding the fundamental
processes by which molecules absorb photons from the laser.
1,4‐Bis (β‐Pyridyl‐2‐Vinyl)Benzene (P2VB) and2,5‐Distyryl‐pyrazine (DSP) asBlue Laser Dyes
Authors: Ebeid E. M. , Sabry M. M. F. , El-Daly S. A.
Published: March 2007

Solutions of P2VB and DSP in dimethyl‐sulphoxide (DMSO) of concentration ca. 10–3 M/l act as laser dyes on pumping with nitrogen laser. P2VB and DSP are lasing
in the ranges 390–440 nm (λmax = 416 nm) and 435–465 nm (λmax = 447 nm) respectively.
An equimolar mixture of P2VB and DSP behaves as an energy transfer dye laser (ETDL)
and is lasing in the range 429–455 nm (λmax = 438 nm). Such ETDL system obeys a
long range coulombic energy transfer mechanism with a critical transfer distance
R0 = 7.5 nm.

The fluorescence quantum yields of both dyes have been measured, and in DMSO
φf = 0.46 and 0.35 for P2VB and DSP respectively.

Both dyes show a remarkable photostability upon nitrogen laser excitation. This has
been attributed to the role of the 337 nm light in inducing a back photo‐chemical
reaction of the initially formed photoproducts consisting mainly of photo‐oligomers
and cis‐photoisomers.
Effective Excitation of High Vibrational States ofSF6 Molecules in a Beam by a Multiple‐frequency IRRadiation
Authors: Apatin Valentin M. , Lokhman Valerii N. , Makarov Grigorii N.
Published: March 2007

Presented here are the first results of experiments
on multiple‐photon excitation (MPE) of molecules
upon their being concurrently irradiated by several
IR pulses differing in frequency. Effective population
of the high vibrational states (HVS) of SF6 was found
to occur even when the frequencies of exciting pulses
were fairly far (10–20 cm–1) from the linear absorption
spectrum (LAS) of the molecules. The method enables one
to obtain narrow vibrational distributions of excited
molecules (VDEM) and make a wider use of the capabilities
of IR lasers for selective photochemistry purposes.
MultiphotonIonization/Fragmentation of SO2:Experimental and ComputationalStudies
Authors: Asscher M. , Guthrie W. L. , Lin T.-H. , Ohmichi N. , Silberstein J. , Levine R. D.
Published: March 2007

The ionic fragmentation pattern of SO2 was measured as a function of laser power at
the 223–220 nm wavelength range. The time of flight (TOF) mass spectrum shows
essentially no parent ions. The principal ions observed were SO+ and mass 32. The
fraction of S+ ions increases monotonically with increasing laser power while the
fraction of SO+ which dominates at low powers reaches a maximum and falls below
that of S+. The fraction of both ions changes nonlinearly with the laser intensity and
tends to level off at the higher powers. The results are found consistent with a statistical
(maximum entropy) computation of the fragmentation pattern. By comparing the
observed (S+ + )/SO+ branching ratio vs. laser power with the computed branching
ratio vs. energy uptake per parent molecule one obtains an energy uptake vs. laser
power curve. The results are discussed in terms of the possible dissociation/ionization
pathways.
Generation of Ketene With HighQuantum Yield by a KrF Laser
Authors: Yunwu Zhang , Fuss W. , Kompa K. L. , Rebentrost F.
Published: March 2007

Acetone was photolyzed around 770 K by pulsed laser irradiation at 248 nm. The methyl
radicals, generated in the primary step, trigger a chain reaction, producing ketene
(CH2CO) and methane. Long chains (high quantum yields) result from low radical
concentrations. Using a collimated laser beam of low intensity, quantum yields up to
300 have been demonstrated. Approximate rate constants have been derived and used
for extrapolation to higher temperatures and different densities. Compared to the thermal
process, the photochemical formation of ketene is faster. Therefore its thermal decomposition
can be avoided to some extent. But the improvement is probably too small to be
of technical interest. We also found indications that the thermal decomposition of
acetone above about 500 to 600 K yields three fragments in a single step.
Effect of the He‐Ne LaserRadiation on the ReproductionRate and Protein Synthesis ofthe Yeast
Authors: Fedoseyeva G. E. , Karu T. I. , Letokhov V. S. , Lobko V. V. , Pomoshnikova N. A. , Lyapunova T. S. , Meissel M. N.
Published: March 2007

The reproduction rate and protein synthesis of the yeast‐like fungus Endomyces magnusii
and yeast Torulopsis sphaerica was studied after the He–Ne laser (λ = 632.8 nm) irradiation.
The synthesis of protein in E. magnusii was activated in dose range from 0.42
to 0.84 J/cm2 with maximum at 0.63 J/cm2. In T. sphaerica the maximal activation took
place at 0.42 J/cm2. The lag‐period was not changed, but the exponential period of the
growth was reduced by 1.5 hours for irradiated cells.
Study of Photoionization ofSolids—Resonance Ionization
Authors: Verdun F. , Muller J. F. , Krier G.
Published: March 2007

Multiphoton ionization (MPI) mechanism in the solid state being still controversial we
coupled a tunable laser to the LAMMA 500 microprobe to reinvestigate, using different
UV irradiations, the ionization of some organic and organometallic solid compounds.
Two polycyclic aromatic hydrocarbons (PAH) anthracene and pyrene and metallic
derivatives of copper and cadmium were tested. Preliminary results are consistent with
thermal desorption of neutral molecules as the first step followed by photoionization
in the vapor phase.

Thus the ionization mechanisms described for gases or vapors, and in particular some
REMPI or RIS processes appear to apply to our experimental conditions.
Laser Photoionization of Potassium Clusters up to K8
Authors: Brechignac C. , Cahuzac Ph.
Published: March 2007

Some features of small potassium clusters Kn, n ≦ 8 are investigated in a crossed laser‐molecular beams experiment
coupled with a time‐of‐flight mass spectrometer. Abrupt
step is found in the mass spectrum for n = 8 when the
ionizing wavelength is higher than the ionization potentials.
Isotopic composition of each mass is observed.
Different behavior in ionization potential spectral
profiles between odd‐ and even‐numbered clusters is shown.
These effects are interpreted in terms of cluster formation
and structures.
Pyrimidine, an Intermediate State Molecule?
Authors: Meerts W. Leo , Majewski W. A.
Published: March 2007

The S1(1B1) ← S0(1A1) transition in pyrazine has been
investigated. High resolution laser induced fluorescence
spectra were obtained by crossing a well collimated
molecular beam with UV radiation of an intra‐cavity
frequency doubled ring laser. The extreme resolution
enabled us to observe the molecular eigenstates of the
electronically excited state. Most of the spectral
features of the S1 state could be interpreted in terms
of a slightly perturbed axis switched rotor spectrum.
The perturbations show up both in the energy levels of
the S1 and in the intensities of the observed transitions.
Influence of Viscous Media on Charge Transfer Reactions
Authors: Tran-Thi T. H. , Koulkes-Pujo A. M. , Mialocq J. C. , Folcher G.
Published: March 2007

The influence of viscous H2O‐Dextran media on two charge
transfer reactions has been investigated using laser
photolysis coupled with pico and nanosecond time resolved
absorption spectroscopy.

In the first case, a charge‐transfer reaction from a
solute (potassium ferrocyanide) to the solvent was
studied and the electron solvation dynamics was followed.
A solvation time delay, depending on the polymer concentration,
is observed which indicates that electrons
remain quasi‐free for longer periods in these media.

In the second case, the quenching process of the triplet
state of an excited metallo porphyrin(ZnP4+) by an electron
acceptor, methylviologen chloride (MV2+, 2 Cl–) is
studied. The measured triplet quenching rate constant
values decrease with increasing dextran concentration,
but remain higher than those calculated, taking into
account a simple viscosity effect. This result is
explained in terms of a competition between a decay
of the diffusion rate constants of (ZnP4+)* and MV2+
due to a viscosity effect and an enhanced cage effect
around the ions (ZnP4+*, MV2+). Once formed, this last
effect favours the charge transfer reaction.
Rotational Energy Distribution of the CsH Formed inthe Reaction Between Cs(7P1/2) and H2
Authors: Visticot J. P. , Ferray M. , D′Oliveira P. , Sayer B.
Published: March 2007

The nascent rotational distribution of the CsH molecules
formed by the reaction between a cesium atom in
the 7P1/2 state and a hydrogen molecule has been measured
in a cell. A thermal distribution at the temperature
of the cell is reported.
Rotationally Inelastic Scattering of Formaldehyde
Authors: Van Hulst N. F. , ter Meulen J. J. , Dymanus A.
Published: March 2007

State to state rotationally inelastic and elastic
differential cross‐sections for the system D2CO‐H2
have been measured at a center of mass energy of 17 meV. A single rotational state of D2CO (110) of high state
purity is focused into the scattering region by combining
rotational cooling and electric state selection.
The final rotational state is probed angle dependent
by LIF using a frequency doubled CW ring dye laser
at 325 nm. The full range of CM angles is probed.
We present the first results of the 110 → 111 inelastic
scattering.
Multiple Photon IR Laser Photophysics and Photochemistry. V
Authors: Bagratashvili V. N. , Letokhov V. S. , Makarov A. A. , Ryabov E. A.
Published: March 2007

This paper ends the series of reviews on multiple photon IR laser photophysics and photochemistry. The applications of IR MP processes in fundamental chemical studies and chemical technology are considered.
Electron Transfer Collisions of Excited Sodium Atoms and Oxygen Molecules
Authors: Desfrancois C. , Astruc J. P. , Barbe R. , Lagreze A. , Schermann J. P.
Published: March 2007

The vibronic network model is here considered for excited sodium atoms and oxygen molecules collisions. Electronic to vibration transfer and reaction cross sections are computed with a single adjustable parameter: the ionic covalent matrix element. The comparison between the atom‐molecule and the quasi‐free electron models is presented.
The Physical Origin of Fitting Laws for Rotational Energy Transfer
Authors: Whitaker B. J. , Brechignac Ph.
Published: March 2007

An historical overview of the various parameterised forms describing RET processes (fitting laws) is presented. The physical models behind these "laws" are compared. Particular attention is paid to the role of angular momentum constraints and to the energy dependence of the state‐to‐state cross‐sections. Finally it is shown how general trends can be inferred from the topology of the intermolecular potential energy surface.
High Resolution Photoionization Spectrum of HBr Measured With Frequency Tripled Laser Radiation
Authors: Munakata Toshiaki , Mizukuki Tadahiko , Misu Akira , Tsukakoshi Motowo , Kasuya Takahiro
Published: March 2007

The photoionization spectrum of HBr around the first ionization limit was measured at
resolution of up to 5 x 10−4 nm. The ionizing vacuum ultraviolet radiation was generated
by frequency tripling of the second harmonic output of a dye laser. Three sets of
Rydberg series, each converging to the ground state (2Π3/2) of HBr+, were observed on
the longer wavelength side of the ionization limit. By extrapolation of the Rydberg
series, the ionization potential of HBr was determined to be 11.666 ± 0.001 eV.