The rapid development of powerful UV-laser sources allows the investigation of macroscopic and microscopic details of elementary chemical reactions important in combustion processes. Experimental results on the effect of selective translational and vibrational excitation of reactants in elementary combustion reactions using laser photolysis and time-resolved atomic line resonance absorption, laser-induced fluorescence and CARS spectroscopy are compared with the results of theoretical studies on ab initio potential energy surfaces and thermal rate parameters. Thermal elimination of hydrogen chloride from 1,2-dichloroethane and 1,1,1-chlorodifluoroethane is a main industrial route to some important monomer compounds. Inducing these radical chain reactions by UV-exciplex laser radiation offers the advantage that a monomolecular process with low activation energy becomes the rate determining step. This allows lower process temperatures with decreasing energy expense and avoiding the high temperature formation of byproducts.

J.  Wolfrum

Laser Induced Chemical Reactions in Combustion and Industrial Processes

A. A. Puretzky

Inverse Electronic Relaxation at IR Multiple-Photon Excitation of Molecules

C. Bradley Moore

Douglas J. Bamford

State-selected Photodissociation Dynamics of Formaldehyde

The effectiveness of various sets of laser frequencies was analyzed for two-frequency MPD of CDF3 molecule at the different pressures of buffer gas. It was shown that MPD yield increased compared to either single-frequency or two adjacent frequencies irradiation.

D. D. Bhawalkar

U. K. Chatterjee

J. P. Mittal

U.  Nundy

V.  Parthasarathy

K. V. S. Rama Rao

S. K. Sarkar

N. S. Shikharkhane

IR MPD of CDF3 in Two-frequency IR Fields

An historical overview of the various parameterised forms describing RET processes (fitting laws) is presented. The physical models behind these &#34;laws&#34; 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.

B. J. Whitaker

Ph.  Brechignac

The Physical Origin of Fitting Laws for Rotational Energy Transfer

Conventional coherent pulse sequences such as photon echoes measure only highly averaged relaxation rates in complex multilevel systems, such as molecules undergoing state-changing collisions. Pulse frequency, phase, and shape control lets us generate sequences which give a more detailed understanding of the dynamics. Results of dual frequency, crafted shape sequences on I2 are presented which show that the &#34;coherence dephasing&#34; time T2 is primarily due to population redistribution (energy changing collisions) in the electronically excited state, and that the electronic ground state has a much smaller cross section for such collisions. Quantitative analysis is only possible with modified laser pulse shapes which excite a single velocity component, and requires pulse sequences which correct for the hyperfine dependence of predissociation. Since this correction is rarely made in previously reported coherent transient measurements, literature values of T2 and T1 may not be reliable in the zero pressure limit.

Mark A. Banash

Warren S. Warren

State-to-State Collisional Dynamics by Coherent Laser Pulse Phase, Shape, and Frequency Modification

Selective photodissociation of diatomic molecules is
used to prepare the separating species in a well defined quantum state with narrowly determined final
kinetic energy of the particles. During the course of
separation to products the repulsive potential is
probed by a tunable dye laser, that is by induced absorption
in case the dissociation proceeds on a potential
leading to ground state products, or by induced
emission or absorption for all other cases. The determination
of interatomic potentials from the observed
spectra is discussed.

H. H. Telle

Stimulated Processes in a Half-collision

The reactions of Ba with CF3I dimers and CH3IAr
complexes were studied applying the laser induced
fluorescence (LIF) technique. It was found that the
BaI produced from the dimers contains about 20
kcal/mole less vibrational energy than the BaI produced
in the corresponding monomeric reaction. The
CH3IAr on the other hand, yielded only a slightly
colder vibrational distribution than the monomers.

R.  Naaman

Vibrational Energy Distribution in B<small.letters>a</small.letters>I Produced in
Reactions of Van der Waals Molecules

Rovibronic spectra of tetracene (C18H12) and its Van der Waals complexes with argon and krypton have been resolved by using a well collimated molecular beam in combination with a single frequency dye laser. The rotational constants of tetracene have been deduced in the S0 and S1 electronic state. The rovibronic spectra of the Van der Waals complexes show an enhanced intersystem crossing.

W. M. van Herpen

W. Leo Meerts

A.  Dymanus

Rotationally Resolved Spectroscopy of Tetracene and its Van Der Waals Complexes With Inert Gas Atoms

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 &#8594; 111 inelastic
scattering.

N. F. Van Hulst

J. J. ter Meulen

Rotationally Inelastic Scattering of Formaldehyde

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.

J. P. Visticot

M. Ferray

P. D&#x27;Oliveira

B. Sayer

Rotational Energy Distribution of the CsH Formed in
the Reaction Between Cs(7P1/2) and H2

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&#x2013;) 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.

T. H. Tran-Thi

A. M. Koulkes-Pujo

J. C. Mialocq

G. Folcher

Influence of Viscous Media on Charge Transfer Reactions

The S1(1B1) &#8592; 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.

W. A. Majewski

Pyrimidine, an Intermediate State Molecule&#63;

Chemiluminescence cross sections for reaction of the individual spin&#8211;orbit states of
metastable Ca(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mrow><mml:mo /><mml:mrow><mml:msubsup><mml:mi>P</mml:mi><mml:mi>J</mml:mi><mml:mn>0</mml:mn></mml:msubsup></mml:mrow><mml:mo /></mml:mrow><mml:mprescripts /><mml:none /><mml:mn>3</mml:mn></mml:mmultiscripts></mml:math>) with CH3I, CH2I2, and SF6 have been determined by the use of optical pumping state selection. This technique was also used to separate the chemiluminescence arising from the two excited metastable Ca 3P0 and 1D states. The spin&#8211;orbit dependence of the chemiluminescence pathway was found to be substantial for the CH3I and CH2I2 reactions and similar to that previously observed for halogen diatom and alkyl bromide reagents. By contrast, no spin&#8211;orbit effect was observed for Ca(3P0)+SF6. These results are discussed in terms of our previously presented model for the origin of spin&#8211;orbit effects in chemical reactions.

Mark L. Campbell

Nick  Furio

Paul J. Dagdigian

The Reaction of Spin&#x2013;Orbit State-Selected Ca(<svg style="vertical-align:-4.66151pt" height="21.65" version="1.1" viewBox="0 0 23.6 21.65" width="23.6" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.012,-0,0,-.012,.062,7.613)"><path id="x33" d="M285 378v-2q65 -13 102 -54.5t37 -97.5q0 -57 -30.5 -104.5t-74 -75t-85.5 -42t-72 -14.5q-31 0 -59.5 11t-40.5 23q-19 18 -16 36q1 16 23 33q13 10 24 0q58 -51 124 -51q55 0 88 40t33 112q0 64 -39 96.5t-88 32.5q-29 0 -64 -11l-6 29q77 25 118 57.5t41 84.5&#xA;q0 45 -26.5 69.5t-68.5 24.5q-67 0 -120 -79l-20 20l43 63q51 56 127 56h1q66 0 107 -37t41 -95q0 -42 -31 -71q-22 -23 -68 -54z" /></g><g transform="matrix(.017,-0,0,-.017,6.4,15.775)"><path id="x1D443" d="M619 482q0 -69 -40.5 -119t-96 -72.5t-118.5 -26.5h-44l-70 20l-31 -151q-14 -67 0.5 -83t89.5 -22l-5 -28h-287l8 28q65 7 81.5 22t29.5 83l79 398q12 56 0.5 70.5t-78.5 20.5l7 28h255q108 0 164 -43t56 -125zM524 478q0 141 -146 141q-25 0 -47 -8q-16 -6 -20.5 -13.5&#xA;t-10.5 -39.5l-43 -241q37 -13 83 -13q67 0 125.5 45t58.5 129z" /></g><g transform="matrix(.012,-0,0,-.012,17.213,7.613)"><path id="x30" d="M241 635q53 0 94 -28.5t63.5 -76t33.5 -102.5t11 -116q0 -58 -11 -112.5t-34 -103.5t-63.5 -78.5t-94.5 -29.5t-95 28t-64.5 75t-34.5 102.5t-11 118.5q0 58 11.5 112.5t34.5 103t64.5 78t95.5 29.5zM238 602q-32 0 -55.5 -25t-35.5 -68t-17.5 -91t-5.5 -105&#xA;q0 -76 10 -138.5t37 -107.5t69 -45q32 0 55.5 25t35.5 68.5t17.5 91.5t5.5 105t-5.5 105.5t-18 92t-36 68t-56.5 24.5z" /></g><g transform="matrix(.012,-0,0,-.012,17.213,19.863)"><path id="x1D43D" d="M434 650l-5 -28q-60 -8 -75 -20.5t-25 -69.5l-71 -395q-20 -107 -57.5 -168t-106.5 -94q-40 -18 -61 -20l-10 32q77 23 113 108q21 50 41 160l68 377q10 57 -1.5 69.5t-76.5 20.5l6 28h261z" /></g></svg>) With CH3I, CH2I2, and SF6

Some features of small potassium clusters Kn, n &#8806; 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 &#61; 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.

C.  Brechignac

Ph.  Cahuzac

Laser Photoionization of Potassium Clusters up to K8

About this journal

Journal profile

Meet the editorial board

Editor spotlight

Submit your proposal

Do you think there is an emerging area of research that really needs to be highlighted? Or an existing research area that has been overlooked or would benefit from deeper investigation? Raise the profile of a research area by leading a Special Issue.

Laser Chemistry