The appearance of CH3+ ions from methyl halides by non-resonant photoionization. A translational energy surprisal analysis. Part I. CH3F

Abstract

A surprisal analysis has been applied to the total translational energy distribution (TED) of CH3+ + F from CH3F giving rise to a new and deeper insight into the dissociation dynamics involved in this process. For both the 16.85 and 21.22 eV photon energies used, the direct population at different energy levels of the B2E state of CH3F+, which is radiationlessly coupled to the repulsive CH3F+ (A2A1) state, gives rise to wide and negatively surprised total TEDs. At both energies they have to be ascribed to severe limitations in the vibrational excitation of CH3+. Additionally, in the case of 21.22 eV photons, a non-statistical expression has to be used to account for the density of translational states. At both photon energies, the population of the CH3F+ electronic states through autoionization of Rydberg states accounts for (i) the concurrent appearance of TEDs governed by a pure RRKM behaviour and (ii) the positively surprised TEDs where the angular momentum conservation plays an important role. At 16.85 eV photon energy the distributions are assigned to CH3F+ (X2E) → CH3+(X1A′1) + F. At 21.22 eV photon energy, doubly excited electronic states of CH3F+ are assumed to take part and they are correlated with CH3+(3A″) + F channel.