Abstract
The applications of high resolution laser techniques to crossed-beam experiments which are examined in this paper concern: (a) the reactivity of atomic/molecular excited states and the influence of light polarization and (b) the measurement of absolute and differential cross sections by use of the laserinduced fluorescence technique performed in a coherent saturation regime.Examples are provided by the crossed-beam study of the Cs(7P) + H2→CsH + H photochemical reaction, where two C.W. single-mode tunable lasers are used to excite Cs atoms and to probe CsH product molecules. It is shown how the fine and hyperfine structures of the Cs atom are involved in the reaction mechanism (harpooning). The measurement of the total cross section (≈4.10−16cm2) gives an indication of the overall efficiency of the reactive process (Cs atoms in the 7P state) with respect to the quenching ones (Cs atoms in 6S, 6P, 5D and 7S states). Finally, the differential cross section shows a marked forward “peaking” of CsH products which narrows with collision energy but which is rather independent of the product rotation.
Highlights
The major aim of reaction dynamics is to observe and to understand the intimate details of chemical reactivity, at the most elementary level of individual, isolated collisions between partners of well-defined energy and orientation
Reaction dynamics involves small systems and simple models which can be extrapolated to reactions of chemical, biological or industrial interest
Lasers are efficient tools to bring selective energy but their use is limited to small systems, the energy deposited in large ones being rapidly randomized
Summary
The applications of high resolution laser techniques to crossed-beam experiments which are examined in this paper concern: (a) the reactivity of atomic/molecular excited states and the influence of light polarization and (b) the measurement of absolute and differential cross sections by use of the laserinduced fluorescence technique performed in a coherent saturation regime. Examples are provided by the crossed-beam study of the Cs(7P) + H2 CsH + H photochemical reaction, where two C.W. single-mode tunable lasers are used to excite Cs atoms and to probe CsH product molecules. It is shown how the fine and hyperfine structures of the Cs atom are involved in the reaction mechanism (harpooning).
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