Photoelectron–photoion coincidence study of the bromobenzene ion

The technique of variable time photoelectron–photoion coincidence mass spectrometry has been applied to the fragmentation of bromobenzene ion producing a phenyl ion. A detailed analysis of the variation of the breakdown curve with parent ion residence time was performed. The results lead to ΔH °_f0 (phenyl ion)=270 kcal/mole in close agreement with recalculated results from an earlier study on chlorobenzene. This, combined with other photoionization results leads to ΔH °_f0 (phenyl radical)=83±3 kcal/mole, slightly higher than the value 80.9±2 kcal/mole obtained from neutral kinetics. The analysis leads to a rate‐energy dependence for the fragmentation process and an equivalent 1000 K Arrhenius pre‐exponential factor of ∼9.4×10¹⁴ sec⁻¹, which may be compared to the value 2×10¹⁵ sec⁻¹ for the analogous neutral process. The possible contribution of spin orbit splitting is discussed.