MECHANISMS AND RATE CONSTANTS FOR THE VIBRATIONAL RELAXATION OF $HD(v=4, 5, and 6)$ IN COLLISIONS WITH HD, He, AND $D_{2}$

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1984

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Ohio State University

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The relaxation of highly vibrationally excited HD with several collision partners is examined using direct overtone excitation and time-resolved photoacoustic detection of the subsequent change in translational energy of the gas. Analysis of such data for $HD(v=4, 5, and 6)$ self-relaxation yields vibration-translation (V-T) and vibration-vibration (V-V) rate constants for collisions between $HD(v=1 to 6)$ and $HD(v=0)$. The V-T rates become larger than the V-V rates above $v=4$. Similarly, relaxation data for the $HD(v=4 and 5)-^{4}$He systems is analyzed and the $HD-^{4}He$ V-T rate constants at $v=4$ and $v=5$ are presented. The differences in the quantum number scaling of the V-T rates for the HD-HD and $HD-{^{4}}He$ systems are discussed. Finally, the time-resolved photoacoustic data for $HD(v=4)$ relaxing in collisions with $D_{2}$ shows the effect of the rapid, near-resonant V-V energy transfer between HD in the $v=1$ through $v=4$ levels and $D_{2}$ in $V=0$.

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Author Institution: Applied Physics \& Materials Laboratory, Department of Mechanical \& Aerospace Engineering, Princeton University; Group CHM-4, MS J567, Los Alamos National Laboratory; Department of Chemistry, Princeton University

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