The effects of isotopomers in the state-selected photofragmentation of BCl3+, PCl3+ and PBr3+

Analysis of the shapes of time-of-flight (TOF) peaks of singly-charged polyatomic cations produced in photoelectron–photoion coincidence spectra allows a determination of the total mean kinetic energy released into translational motion of the fragment species, 〈KE〉t. In turn, this value can indicate the mechanism of unimolecular photofragmentation. We show that in cases where the daughter ion has more than one isotopomer, allowance must be made for them in analysing the TOF distributions. Otherwise, values for 〈KE〉t are obtained which are too large. Examples are given from recent work by us on state-selected (BCl3+)∗→BCl2++Cl and (PX3+)∗→PX2++X (X=Cl,Br).