Resonance and reversibility of vibrational relaxation of HF in high temperature Ar bath gas

Abstract

The Boltzmann averaged rate constants for total vibrational relaxation of HF(vϭ1) in collisions with Ar are computed in the range of temperatures between 100 and 1500 K. The computed rate constants overestimate the experimental measurements at high temperatures by a large factor. It is concluded that the deviation between theory and experiment cannot be explained by inaccuracy of the PES or dynamical approximations made. It is shown that increasing initial rotational energy enhances a resonant character of the vibrational energy transfer to a great extent. An assumption is made that total vibrational relaxation of HF(vϭ1) at high temperatures is determined by competition between vibrational relaxation to a resonant level (vϭ0,j res), vibrational excitation from the resonant level, and purely rotational relaxation of HF(vϭ0,j res). It is demonstrated that at high temperatures the latter process can be significantly slower than vibrationally inelastic transitions and rotational relaxation of HF(vϭ0,j res) may in fact be a rate-limiting stage of vibrational relaxation.

Theoretical study on quantum dynamics for Ar-HF inelastic collision

“…FIG. 4 shows the rate constant of this work together with the calculated result by Krems et al [19] and various measured results [9−14]. As mentioned above, the experimental rate constants at low temperatures are inaccurate, while they are reliable at high temperatures.…”

“…As the counterpart, early theoretical studies attempted to calculate these quantities by using quasi-classical trajectory (QCT) and infinite-order sudden approximations (IOSA) methods [16−18] based on a pairwise additive potential. Later, Krems et al [19,20] and Shroll et al [21] reported the ICSs for rotational transition of HF (v=0, j=0) at some low collision energies, using the coupledstates approximation (CSA). However, these theoretical results agree with the experiment only in trend and can only qualitatively reproduce the experimental ones.…”

“…calculated the state-to-state vibrational relaxation ICSs for the HF initial state of (v=1, j=0) and quasi-resonant features were found in this system. Besides, Krems et al [19] calculated the rate constants via different potential energy surfaces (PESs) by using the CSA method, from 100 K to 1500 K. Unfortunately, all the previous calculated vibrational-resolved rate constants deviate significantly from the experimental data at all temperatures.…”

70 years of Landau–Teller theory for collisional energy transfer. Semiclassical three-dimensional generalizations of the classical collinear model

“…(ii) There exist quantum CS calculations 107,108 which provide some possibility for comparison with the HR and EM results.…”

“…(iii) Unfortunately the available experimental data do not allow for an unambiguous interpretation in terms of state-tostate rate coefficients (see below). 108 In this case, we refrain from comparing the theoretical and experimental values of k 10 and concentrate on a comparison of theoretical values of k 10 from the numerical CTC HR calculations of 1985 employing the best available PES at that time, k CTC-HR 10 , with numerical CS calculations of 2002 with two more recent ab initio PES, k CS 10 . We also verify qualitative predictions of the HR model about the distribution of the released energy over translational and rotational degrees of freedom.…”