Imaging CIN3 photodissociation from 234 to 280 nm

Abstract

We report Cl(²P_3/2) and Cl*(²P_1/2) fragment images following ClN₃ photolysis in the 234–280 nm region measured by velocity map imaging. Kinetic energy distributions change shape with photolysis wavelength from bimodal at 234 and 240 nm to single peak at 266 and 280 nm. Where two peaks exist, their ratio is significantly different for Cl and Cl* fragments. The single peak of 266 and 280 nm and the faster peak at 234 and 240 nm are assigned to a Cl + linear-N₃ dissociation channel, in agreement with previous work. The slow peak in the bimodal distributions is assigned to the formation of a high energy form (HEF) of N₃. Candidates for the identity of HEF-N₃ are discussed. Combining our data with photofragmentation translational spectroscopy results, we determined the threshold for the appearance of HEF-N₃ at 4.83 ± 0.17 eV photolysis energy. This threshold behavior is similar to recently reported results on the wavelength dependence of HN₃ photolysis, where the threshold was associated with a ring closed isomer of HN₃ on the S₁ potential energy surface. We also note that the HEF-N₃ formation threshold observed for ClN₃ occurs where the energy available to the products equals the isomerization barrier from linear to cyclic-N₃.