Electron ionization cross-section and fragmentation of α-cyclohexanedione

Abstract

Electron ionization cross-section and fragmentation behavior of a volatile organic compound, 1,2-Cyclohexanedione (α-CHD) have been studied. Intact molecular ion is the major feature of the mass spectrum at low electron kinetic energy. However, with increasing energy of the ionizing electrons, molecular ion signal monotonically decreases and the fragment ions display some interesting variations. Three primary fragmentation channels, carbon monoxide and ketene losses and symmetric cleavage of the molecular ion have been identified. The ionization cross-sections of α-CHD have been estimated relative to that of molecular oxygen for electron kinetic energy in the range of 10–30 eV. Total ionization cross-section of the molecule has been estimated to be of the order of ∼10⁻¹⁶ cm²/molecule. Electronic structure calculation at DFT/B3LYP/6-311++G** level has been performed for structural information of the intact molecular and fragment ions, and to calculate the thermodynamic parameters associated with various reaction channels. The predictions are found to useful to interpret the fragmentation spectra as a function of electron kinetic energy.