Interpretation of the vibrational relaxation of H2 in H2 within the semiclassical effective mass approach

Abstract

The temperature dependence of the rate coefficients for vibrational relaxation of H2 in neat H2 is interpreted within the semiclassical effective mass approach. Across the temperature range of 80-3000 K, the experimental rate coefficients vary by five orders of magnitude and fall onto a strongly nonlinear Landau-Teller plot. This behavior is explained by the nonclassical nature of the energy release and by a substantial participation of rotation of the colliding partners in inducing the vibrational transition. A single fitting parameter, the optimal reduced mass, permits one to represent the temperature dependence of the rate coefficient within a factor of 2. This parameter is found to be close to that obtained from a simple model suggested by Sewell et al. [J. Chem. Phys. 99, 2567 (1993)].

Collisional excitation of water in warm astrophysical media

“…Below 1500 K, however, the T −1/3 dependence does not hold. This finding was observed in many other hydrogen systems as demonstrated by strongly nonlinear Landau-Teller plots (see for example the theoretical work of Dashevskaya et al (2007) for H 2 +H 2 ). Furthermore, even negative temperature dependence was observed experimentally close to room temperature for the self-relaxation of H 2 O (Zittel & Masturzo 1991).…”

Cross Sections and Reaction Rates for Comparative Planetary Aeronomy

“…Comprehensive accurate chemical dynamics calculations have not been completed for this very complex system with four active atoms, nine active electronic states, and multiple potential surface crossings. Additional theoretical guidance comes from the recent studies of vibrational relaxation at low temperature by Nikitin and Troe (Dashevskaya and Nikitin 2000;Dashevskaya et al 2003Dashevskaya et al , 2006Dashevskaya et al , 2007Nikitin and Troe 2006). They point out that quantum mechanics (Bethe 1937;Wigner 1948;Dashevskaya et al 2003) implies the surprising conclusion that exoergic deexcitation reactions can have non-zero rate coefficients as the temperature approaches zero, in contrast to the normally expected T 1/2 dependence, as long as the interaction potential energy surface is attractive.…”