The 248 nm Photodissociation of ClNO₂ Studied by Photofragment Translational Energy Spectroscopy

The photodissociation of nitryl chloride (ClNO2), a potentially active species in atmospheric chemistry, has been studied following excitation into the weakly structured band at 248 nm using photofragment translational energy spectroscopy. Among the energetically accessible decay channels, only the formation of the primary fragments Cl + NO2 has been found to be active involving the fission of the weakest bond (D0(Cl−NO2) = 138 kJ/mol). The two fragments exhibit a well-structured translational energy distribution. The structure is attributed to different decay routes which include the formation of NO2 fragments in different electronic states. Thus, about 30% are produced in the ground state while the rest, in accordance with the kinetic energy structure and the available fragment energy, is consistent with production in the A2B2 and B2B1 excited electronic states. The similar rovibrational energy channeled into NO2 along the three decay routes suggests an indirect decay with an exit barrier. In addition, at high laser fluences secondary photodissociation of the hot or electronically excited NO2 products to NO + O was observed.