Ab initio study of the chloromethane dication fragmentation

Abstract

The chloromethane dication dissociation pathways have been studied using the complete active space self-consistent field (CASSCF) method followed by a multi-reference perturbative configuration interaction (CI). The vertical double ionization energy is calculated to be 31.64 eV for the first singlet state and 30.69 eV for the first triplet state, the latter value being close to the experimental determination of 31.5 ± 0.5 eV. For most two-body dissociation processes, the appearance thresholds of the ion pairs observed in coincidence experiments are in good agreement with the results of the calculations. In the case of the CCI +/H 3 + pair, the dissociation is indirect and comes from the ionization of a Rydberg excited state of the CH 3CI + monocation. For three-body processes, the uncertainties of the available experimental results and the large number of possible dissociation channels do not allow identification uniquely of the involved mechanisms in most cases.