DIRECT MEASUREMENT OF $\Delta J = n$ PROCESSES IN METHYL FLUORIDE
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Date
1989
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Ohio State University
Abstract
A millimeter / submillimeter - infrared double resonance technique was used to study $\Delta J = n$ processes in $^{12}CH_{3}F$ and $^{13}CH_{1}F$. In this experiment a Q-switched $CO_{2}$ laser populated a unique ro-vibrational level in the $V_{3} = 1$ vibrational state of methyl fluoride. The time responses of the strengths of many rotational lines within the $V_{3} =1$ manifold were monitored. Outside the K-stack containing the pumped level, the time responses were well understood as being the result of the $\Delta K = 3n$, vibrational swap, and vibrational relaxation mechanisms. Within the same K-stack as the pumped level the early time responses displayed the additional effects of $\Delta J = n$ processes. A numerical simulation of rotational energy transfer has been developed to describe rotational energy transfer in either isotope of methyl fluoride. The key experimentally verified assumption of this simulation was that all states within a given symmetry type are in rotational equilibrium. The Jone exception to this rule involved those stases within the same K-stack as the pumped level. Therefore, the simulation described energy transfer among two pools (one representing each symmetry type) and the many rotational levels of the K-stack containing the pumped level. The simulation was used as a basis for a nonlinear least squares fit of the experimental data in order to extract the rates of the $\Delta J = n$ processes. The $\Delta J = 1-5$ rates were measured for $^{13}CH_{3}F$, and the $\Delta J = 2-10$ rates were measured for $^{12}CH_{3}F$.
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Author Institution: Department of Physics, Duke University