The deconvolution of experimental V→T rate constants: He-H2, H2-H2, and D2-D2*

A 5-parameter hyperbolic representation for V→T cross sections which is sufficiently flexible to fit accurately a series of recent theoretical cross sections is presented. This representation is used to deconvolute low-temperature V→T rate constants for H2-H2, H2-He, and D2-D2. The scatter in the experimental He-H2 points results in considerable uncertainty in the cross section below E approximately 0.04 eV. For H2-H2 there is a pronounced minimum in the V→T cross section at E approximately 0.015 eV which is absent for D2-D2. Extrapolation to higher temperatures predicts relaxation times which are significantly less than the values given by shock-tube studies, which suggests that vibrational relaxation occurs faster than the process detected by these experiments. The present results suggest that a log-log, rather than Landau-Teller, plot of experimental V→T data may allow a more meaningful theoretical interpretation. (Auth.)