Temperature dependence of the quantum yields for the photolysis of NO₂ near the dissociation limit

Photolysis quantum yields for NO₂ + hv → O(³P) + 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 ≈10% at 400 nm and ≈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.