Nonequilibrium Effects in Atomic Recombination Reactions

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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.