Vibrational relaxation in gaseous SiF4 by Ar and Ne at 304 K

Abstract

A computer-controlled ultrasonic interferometer has been utilized for exploring room-temperature relaxation of gaseous SiF4–Ar and SiF4–Ne mixtures. A single relaxation process was observed for all mixtures, and the relaxation rates, 1/pτ, were found to vary linearly with the mole fraction of added argon or neon. Analysis of the mixture relaxation data shows that collisions between SiF4 molecules and either Ar or Ne atoms are less efficient for V−T transfer than are SiF4 self-collisions. This result can be explained within the Schwartz–Slawsky–Herzfeld formulation if it is assumed that a steep repulsive potential (i.e., the 7:28 function) is operative for SiF4–SiF4 collisions, while the repulsive interaction for SiF4–noble gas collisions is treated as being between a molecule obeying a 7:28 law and an atom characterized by a 6:12 function.