Reaction of O(1D) with CO

Abstract

The photolysis of O3 in liquid CO at 77°K has been studied with 2537-Å radiation. Carbon dioxide is formed with a quantum yield of 0.07 and in a 1:1 ratio with O3 disappearance. The CO2 quantum yield is reduced by addition of N2, O2, or Ar, but is increased by lowering the temperature of the solution. Formation of CO2 is attributed to the reactionO(1D)+CO(+M)→CO2(+M),and the low quantum yield is believed to be caused by the reactionO(1D)+CO+M→CO+O(3P)+Mwhich leads to O3 reformation. The reaction of O(1D) with CO is an example of an association process in which the excited association complex may undergo unimolecular decomposition to products of lower electronic energy in the course of stepwise vibrational deactivation. Formation of the association product is of higher order than one with respect to M, the actual order depending on the number of vibrational states in which unimolecular dissociation competes with collisional deactivation. Because of the high-order dependence on M, the rate of product formation is very sensitive to the deactivation efficiency of the third body. The effect of added diluents is believed to arise partly from competition of the added diluents for O(1D) and partly from the resulting change in solvent deactivation efficiency. The effect of reduced temperature is attributed to an increased rate of deactivation resulting from an increased solvent density.