The dissociation of state-selected CF3X+molecular ions

Abstract

Dissociations of state-selected ions of CF3 X + (X = F, Cl and Br) have been studied by a photoelectron-photoion coincidence technique. The identities of the product species and kinetic energy release distributions for these fragmentations are obtained from ion time-of-flight measurements. It is shown that the behaviour of the CF3 X + ion is strongly dependent upon its electronic state. The energy releases are generally in accordance with an impulsive dissociation model and instances of prior transitions to lower lying electronic states are found. From the magnitude of the energy releases it is possible to assign upper limits for the dissociative ionization thresholds of (a) CF4 + → CF3 + + F + e- and (b) CF3Cl+ → CF2Cl+ + F + e- as 14·7 ± 0·3 eV and 14·0 ± 0·3 eV respectively. Anomalous behaviour arises when ~A 2 A 1 CF3Cl+ is prepared with HeI radiation. A second dissociation channel appears, characterized by a smaller kinetic energy release, although both channels apparently lead to the same product ion, ~X 1 A 1 CF3 +. The distribution of kinetic energy in the second channel is consistent with a statistical dissociation, whilst that in the first channel suggests a direct dissociation. It is shown that this behaviour most probably follows autoionization of CF3Cl at the HeI wavelength and the implications of this are further considered.