V→T, R energy transfer in HCl- and DCl-rare gas mixtures

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Abstract
Vibrational relaxation rates have been measured for HCl and DCl in collisions with the rare gases 3He, 4He, Ne, and Ar. For mixtures with 4He and Ar, data are given between 295 and 700°K. The rates vary approximately linearly with T−1/3 indicating that hard collisions cause the relaxation. The value of PHCl–Ar/PDCl–Ar=2 is evidence that nearly all of the vibrational energy is transferred into rotation in collisions with Ar. As the mass of the rare gas decreases, PHCl–M/PDCl–M decreases. PHCl–3He/PDCl–3He=0.6. This indicates an increasing importance of translational motion. Substitution of reasonable parameters into a simple theory of V→T, R energy transfer gives qualitatively the same behavior as the experimental results. The wide range of reduced masses, the isotopic substitution of 3He for 4He, the comparison of HCl and DCl, and the temperature variation make an ideal set of data for testing more complete theories of V→T, R energy transfer in atom-diatom collisions.

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