Heat of formation for the propanoyl cation by photoionization mass spectrometry

The ionization energies and [C 3 H 5 O] + appearance energies for a series of oxygenated organic compounds have been measured by dissociative photoionization mass spectrometry. The adiabatic ionization energy for cyclopentanol is observed to be 9.72 eV. A 298 K heat of formation of 591.2±2.3kJ mol −1 , based on the stationary electron convention, is derived for the propanoyl cation in the gas phase. A heat of formation of –86±6 kJ mol −1 is obtained for methylketene, which leads to an absolute proton affinity of 853±8 kJ mol −1 .