Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation

The photodissociation dynamics of ClONO2 at 235 nm has been reinvestigated using velocity map ion imaging. We report branching ratios for the Cl + NO3 and ClO + NO2 channels to be 0.49:0.51 with anisotropy parameters of β = 0.5 ± 0.1 and β = −0.1 ± 0.3 for the Cl and ClO production channels, respectively. Photodissociation at 248 nm and 262 nm results in similar branching ratios and dynamics as observed at 235 nm. Measured O(3P2) images arising from ClONO2 dissociation at 226 nm suggest that oxygen atoms result from the spontaneous dissociation of metastable NO3. The quantum yield of O atoms arising from the spontaneous dissociation of NO3 varies from 0.09 at 262 to 0.38 at 235 nm based on the derived internal energy distributions of the NO3 fragments. We also describe a Monte-Carlo forward-convolution fitting of imaging data which permits detailed analysis of both spontaneous secondary dissociation and secondary photodissociation.