Cl-Loss dynamics in the dissociative photoionization of CF3Cl with threshold photoelectron–photoion coincidence imaging

Abstract

The dissociative photoionization of CF₃Cl was investigated in the photon energy range of 12.30–18.50 eV. The low-lying electronic states of CF₃Cl⁺ cations were prepared by the method of threshold photoelectron–photoion coincidence (TPEPICO). The threshold photoelectron spectrum and the coincident time-of-flight mass spectra at the specific photon energies were recorded. Only a CF₃⁺ fragment was observed at lower energy, while a CF₂Cl⁺ fragment appeared for C²E and D²E states. As Cl-loss from the ground ionic state is statistical, the total kinetic energy release distribution (KERD) is represented as a Boltzmann profile, and a 0 K appearance energy of AP₀ =12.79 ± 0.02 eV is derived from the statistical modelling of the breakdown diagram from 12.60 to 12.85 eV without taking into account the kinetic shift. For the A²A₁ and B²A₂ states of CF₃Cl⁺ cations, the total KERDs are bimodal, where a parallel faster dissociation appears together with the statistical distribution. At higher energies like the C²E and D²E ionic states, a bimodal distribution similar to that of the A²A₁ and B²A₂ states is also observed for the KERD. With the aid of the calculated Cl-loss potential energy curves, the dissociative mechanisms of internal energy-selected CF₃Cl⁺ cations are proposed.