Heat of formation for the benzoyl cation by photoionization mass spectrometry.

Dissociative photoionization mass spectrometry has been used to measure the PhCO(+) appearance energies for several benzoyl compounds. Based on these threshold measurements, an experimental 298 K heat of formation of 738.8 -/+ 3.3 kJ mol(-1) is obtained for the benzoyl cation. The experimental results are supported by high-level ab initio calculations.