Heat of Formation for the Methylenimmonium Cation by Photoionization Mass Spectrometry

Abstract

Photoionization mass spectrometry has been used to measure the CH2NH2+ appearance energies for six primary amines, resulting in a 298K heat of formation of 749.5 ± 1.3 kJ mol−1 for the methylenimmonium cation. An absolute proton affinity of 868.8 ± 2.5 kJ mol−1 is derived for methylenimine. Based on experimental data for ethylenediamine, the 298 K heat of formation for the aminomethyl radical is found to be 153.6 ± 1.7 kJ mol−1. These results are supported by high-level ab initio calculations.