ENERGY ABSORPTION AND VIBRATIONAL HEATING IN MOLECULES FOLLOWING INTENSE LASER EXCITATION

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1976

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Ohio State University

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Resonant absorption of energy from an intense laser pulse and its distribution in high vibrational states of the absorbing molecules have been studied in the regime where V-V collisions populate high-lying vibrationa1 states. The model assumes that the pulse duration $T_{p} \gg T_{vv}, T_{vt} \gg T_{p}$, and that the pulse equalized $n_{0}$ and $n_{1}, n_{v}$, being the population of $|v{>}$. The number of absorbed quanta/mol. is then calculated to be $(1 - n_{1})^{2}$, with $1/n^{2}_{1} + 4(1n \ 2n_{1}) = 4 + T_{p}/T_{vv}$. To test the theory, the absorption of a 0.1J 2-4 $\mu$sec P(32) $CO_{2}$ laser pulse by the $\nu 3(v =0 \rightarrow 1)$ fundamental of $CH_{3}F$ is being studied. The observed absorption of 2-3 quanta/mol. implies $T_{vv} \sim 1 \ \mu$sec-Torr, Evidence that all energy goes into vibrations has been obtained by measuring the vibrational temperature $(T_{v})$ using a new laser-induced fluorescence technique. Measurements show $T_{v} \simeq 2000^\circ K$, in good agreement with model.

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$^{1}$ C. R. Jones and H. P. Broida, J. Chem. Phys. 60, 4369 (1974). This work was supported, in part, by the Air Force Office of Scientific Research and the National Science Foundation.
Author Institution: Massachusetts Institute of Technology; Los Alamos Scientific Laboratory, Univeresity of California; Los Alamos Scientific Laboratory, Columbia University

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