The H+para-H2 reaction: Influence of dynamical resonances on H2 (v′=1, j ′=1 and 3) integral cross sections

Abstract

We have measured integral rate constants for the reaction H+para-H2→H2(v′=1, j′=1 and 3)+H at 11 center-of-mass collision energies (Erel) between 0.88 and 1.01 eV, a region in which dynamical scattering resonances are present. We have also measured the H2(v′ = 1, j′ = 3)/H2(v′ = 1, j′ = 1) population ratio at two additional values of Erel outside of this range. Tunable uv laser photolysis of HI was used to generate translationally hot H atoms of variable kinetic energy. Quantum-state-specific detection of the H2 reaction product was accomplished via (2+1) resonance-enhanced multiphoton ionization and time-of-flight mass spectrometry. The integral rate constants have a smooth dependence on Erel, in agreement with the recent quantum-mechanical (QM) calculations of Zhang and Miller and contrary to the experimental results of Nieh and Valentini. The QM results are in nearly perfect agreement with the present measurements for the dependence on Erel of both the integral rate constants and the H2(v′ = 1, j′ = 3)/H2(v′= 1, j′ = 1) population ratio. It is concluded that measurements of integral cross sections as a function of collision energy are not highly sensitive to the presence of dynamical resonances in this system.