Nonequilibrium Effects in Atomic Recombination Reactions

Abstract

Relaxation in the bromine-argon system is investigated by approximating the time evolution with a sequence of trajectory calculations. Two systems are considered: (a) recombination of bromine atoms via the radical-molecule complex mechanism and (b) rotational relaxation of a rigid rotator in a thermal bath. The phenomenological and equilibrium rate coefficients for recombination at 300°K are computed and compared. Nonequilibrium effects lead to a 19% discrepancy between the two rate coefficients after an initial transient period during which the phenomenological rate coefficient shows a distinct time dependence. Comparison of the rotational relaxation of Br2 and the rigid rotator shows the importance of vibrational-rotational coupling for highly excited molecules. The relaxation time of the vibrationally excited molecules is much greater than that of the rigid rotators.