Fragmentation of acetic acid ions with selected internal energies

Abstract

The unimolecular dissociation of acetic acid ion in the photon energy range 10.5–17.0 eV was studied using threshold photoelectron photoion coincidence mass spectrometry. The detailed breakdown graph was obtained and the fragmentation pathways were elucidated. The breakdown graph calculated using statistical theories was found to be consistent with the experimental data up to a photon energy of about 12.5 eV. The average kinetic energy release observed is higher than that calculated on the basis of quasi-equilibrium theory for the formation of COOH + while it seems to be statistical for the formation of CH 3CO +. The origin of kinetic energy release accompanying the formation of these two ions is discussed. The structure of [COH 3] + ion ( m/z 31) is determined to be hydroxymethyl cation, CH 2OH +, which could be formed by a two-step rearrangement prior to dissociation.