Dissociative photoionization of β-pinene: An experimental and theoretical study

We investigated the photoionization and dissociation photoionization of the β-pinene molecular using time-of-flight mass spectrometry with a tunable vacuum ultraviolet source in the region from 8.00 eV to 15.50 eV. The experimental ionization energy (IE) value is 8.60 eV using electron impact as the ionization source, which is not in good agreement with theoretical value (8.41 eV) with a G3MP2 method. We obtained the accurate IE of β-pinene (8.45 ± 0.03 eV) derived from the efficiency spectrum, which is in good agreement with the theoretical value (8.38 eV) of the CBS-QB3 method. We elucidated the dissociation pathways of primary fragment ions from the β-pinene cation on the basis of experimental observations in combination with theoretical calculations. Most of the dissociation pathways occur via a rearrangement reaction prior to dissociation. We also determined the structures of the transition states and intermediates for those isomerization processes.