Investigation of vacuum ultraviolet photoionization of methylcyclohexane in energy region of 9−15.5 eV

Vacuum ultraviolet (VUV) photoionization and photodissociation of methylcyclohexane have been studied utilizing a reflectron time-of-flight mass spectrometer (RTOF-MS) with synchrotron radiation source. Photoionization efficiency curves (PIEs) of molecule ion C 7 H 14 + and fragment ions C 7 H 13 + , C 6 H 11 + , C 6 H 10 + , C 5 H 10 + , C 5 H 9 + , C 4 H 8 + , C 4 H 7 + , and C 3 H 5 + were observed. The ionization energy of methylcyclohexane was measured to be (9.80±0.03) eV, and appearance energies of fragment ions were determined from the PIEs. Optimized structures of transitional states, intermediates and product ions were characterized at the B3LYP/6-31G(d) level and the energies were calculated using G3B3 method. Formation channels of dominating fragment ions were proposed. Intramolecular hydrogen migrations and carbon ring-opening were the foremost processes in fragmentation pathways of methylcyclohexane.