TEMPERATURE-DEPENDENCE OF THE QUANTUM YIELDS FOR THE PHOTOLYSIS OF NO2 NEAR THE DISSOCIATION LIMIT

Photolysis quantum yields for NO2 + hv --> O(P-3) + NO are reported for the wavelength range 388-411 nm at two temperatures (248 and 298 K). At room temperature, the quantum yield is found to be (0.93 +/- 0.10) from 388 to 398 nm and to decrease smoothly to a value of 0.12 at 411 nm. Beyond the dissociation threshold (397.9 nm), quantum yields obtained at 248 K are found to be significantly lower than those at 298 K (by approximate to 10% at 400 nm and approximate to 50% at 411 nm). The observed quantum yield data beyond the thermodynamic threshold are explained quantitatively in terms of a mechanism involving both direct dissociation (through the use of internal rovibrational energy) and dissociation of excited NO2 induced by Collisions with the bath gas.