Collisional Deactivation of Excited Oxygen Atoms in the Photolysis of NO2 at 2288 Å

The isotopic composition of the oxygen produced from the 2288-Å photolysis at room temperature of NO2 in the presence of C18O2 has been measured as a function of the pressure of various additive gases. A simple reaction mechanism involving reactions of excited oxygen atoms is postulated to explain the results and leads to the following relative rates of electronic deactivation (including chemical reaction, where possible) of the excited atoms: CO2, 1.00; Ar, 0.01; Kr, 0.06; Xe, 0.78; N2, 0.24; N2O, 1.02; NO2, 1.62; C3H8, 4.67; and SF6, close to zero. The close correspondence of these relative rate constants to the values obtained from studies of the photolysis of N2O at 1849 Å suggests that the results for the photolyses of both N2O and NO2 refer to the same species of excited atom, namely O(1D2).