THE USE OF LASER TECHNIQUES TO PROBE THE ENERGETICS OF REACTION PRODUCTS THE Cs(7P) + H2 REACTION

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THE USE OF LASER TECHNIQUES TO PROBE THE ENERGETICS OF REACTION PRODUCTS THE

Cs(7P) + H2 REACTION

G. Rahmat, J. Vergès, R. Vetter

To cite this version:

G. Rahmat, J. Vergès, R. Vetter. THE USE OF LASER TECHNIQUES TO PROBE THE EN-

ERGETICS OF REACTION PRODUCTS THE Cs(7P) + H2 REACTION. Journal de Physique

Colloques, 1987, 48 (C7), pp.C7-689-C7-689. �10.1051/jphyscol:19877169�. �jpa-00226992�

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JOURNAL DE PHYSIQUE

Colloque C7, supplgment au n012, Tome 48, dgcembre 1987

THE USE OF LASER TECHNIQUES TO PROBE THE ENERGETICS OF REACTION PRODUCTS THE Cs(7P) + H, REACTION

G. RAHMAT, J.

VERGBS

^andR . VETTER

Laboratoire Aim6 Cotton, CNRS JI, F-91405 Orsay Cedex, France

The reaction of cesium atoms w i t h hydrogen molecules is hig.dy endoergic i n t h e ground s t a t e (AH-2.7 eV) but c a n proceed a f t e r electronic excitation of C s atoms t o t h e 7P s t a t e : Cs(7P)+ H , + CsH+H. I n this case, t h e potential energy above threshold i s drastically s m a l l : 0.0016 eV f o r a C S ( ~ P ~ / ~ ) excitation and 0.024 eV f o r a c S ( ~ P ~ / ~ ) excitation. This system a t threshold is thus very a t t r a c t i v e t o study t h e influence upon reactivity of various parameters, if high resolution techniques a r e w e d , both t o prepare reagents and t o characterize reaction products.

This is achieved by the com bined use of supersonic beams of particles and* C.W. tunable laser beams. In our experiment, a supersonic beam of hydrogen and a supersonic beam of cesium atoms cross a t right angle ; perpendicularly t o t h e plane of collisions, a f i r s t l a s e r beam is used t o excite C s atoms (6S112 + 7P1/2,3/2) and a second one is w e d t o excite C s H molecules

( X ( ~ E + , V1l=~,jll) + A(*E+, Vf=5J1)). The fluorescence light due t o C s H molecules is

then collected and analyzed through a photon-counting device ; a slow scanning of t h e second l a s e r frequency yields t h e high resolution s p e c t r a l profile of t h e signal.

For this particular system, one has g e t :

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t h e rotational distribution of products, a t c o d t a n t incident energy.

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t h e variation of jfl- resolved cross sections with kinetic -energy.

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f m t indications concerning t h e energetics of products : velocities and angular dispersion.

More specifically, high resolution studies of Doppler profiles associated t o recoil velocities acquired by products i n t h e c e n t e r of mass lead t o a complete evaluation of the various forms of energy, t h e n t o t h e accurate determination of t h e reaction threshold and, furthermore t o t h e angular dispersion of Products. It is shown t h a t this angular distribution is strongly forward peaked song relative velocities, although t h e relative arrangement of particle beams and laser beams is not favorable f o r t h e study of Doppler effect. More favorable geometries are on study t o improve t h e sensitivity of t h e method which could be

COm petitive with other methods of detection such a s m a s s spectrometry.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19877169