Fragmentations of singly charged ethanol cation: An ab initio/RRKM study

A theoretical study was performed to investigate the probable fragmentation channels of a singly charged ethanol radical to represent the signals of m/e 45, 31, 44, 32, 30 and 28, found in the related mass spectra. The related fragments as implied in the mass spectra should originate from conformers of CH3CH2OH+ through the H-elimination channels. In order to obtain reasonable rate constants, it is necessary to include the anharmonic frequencies in RRKM method to eliminate the unrealistic rotational mode in the transition state. Most of the C2H6O+ isomerization reactions require more energy than the abstraction of methyl group and hydrogen atom from CH3CH2OH+. Consistent with experimental observation, at low energy, the H-abstraction channels are preferred due to the low energy barriers, while, at high energy, and the methyl abstraction channels are dominated. The fragments with formation energy barriers from high to low are CH2CH2+, CH2O+, CH2CHOH+ and CH2OH2+ accordingly, also in a good agreement with experimental observation.