Photolysis of SO 2 in the presence of foreign gases IV. Wavelength and temperature effects with CO

Abstract

Studies of the photolysis of SO 2 in the presence of CO have been extended (from 3130 Å and 300 K) to 2537 and 3261 Å at 300 K, and to 415 and 520 K at 3130 Å. Experiments were also performed in the presence of either or both of No and N 2. The quantum yield for CO 2 formation, Φ{CO 2}, is independent of temperature and the absorbed intensity, but shows a mild wavelength dependence. At high SO 2 pressures, Φ{CO 2} is nearly independent of [SO 2] and directly proportional to [CO]. At lower SO 2 pressures, Φ{CO 2} increases with decreasing [SO 2]. Φ{CO 2} is markedly reduced by the addition of small amounts of NO, but is not zero. The addition of a large excess N 2 gives only a slight reduction in Φ{CO 2}. Further experimental evidence is provided for the non-emitting singlet and triplet states. The results are fitted with a three electronic state model of two excited singlets (one emitting and one non-emitting) and the non-emitting triplet state. A set of rate constants is obtained which is consistent with all the spectroscopic data and satisfactorily fits almost all of the 216 data points at 300 K as well as those at elevated temperatures.