Quenching and excitation transfer for the c 3Π u- and a 3Σg+ states of H2 in collisions with H2

Abstract

Collisional destruction rate coefficients for c 3Π u- metastable states by thermal energy hydrogen molecules have been measured for various vibrational and rotational levels (N = 1, v = 0,1,2,3 and v = 1, N = 1,2,3). The rate coefficients were found to be independent of vibrational and rotational quantum number and had a mean value of (1.88±0.10)x10-15 m3 s-1 at 300 K. Destruction rate coefficients and radiative lifetimes of the a 3Σg+ state have also been measured. Collisional quenching rate coefficients at 300 K of (11.5±1.0) and (6.3±0.8)x10-16 m3 s-1 were obtained for the v=0 and 1 levels, respectively. Radiative lifetimes of 11.1±0.3 ns for v=0 and 10.4±0.3 ns for a 3Σg+ (v = 1) are in good agreement with recent experiment and theory. Collisional excitation transfer between the N = 1 levels of the a3Σ g+ and c3Πu- states was observed for v = 0 and 1. No Collisional excitation transfer between other a3Σg+ and c 3Π u- levels or between two c 3Π u- levels was detected. Measured fractional absorption signals and detailed balancing arguments were used to determine the excitation transfer rate coefficient for the v = 1, N = 1 level of the a 3Σg+ state to the v = 1, N = 1 level of the c 3Πu- state as (3±2)x10-16 m3 s-1 and that for the reverse process as (1.8±1)x10-16 m3 s-1 for a calculated gas temperature of 410 K. Excitation transfer to the c 3Π u state and subsequent rapid quenching accounts for a large fraction, if not all, of the collisional quenching of the a 3Σ g+ (v = 1, N = 1) state. © 1988 American Institute of Physics.