Vibrations of the low energy states of toluene (X super(1)A sub(1) and A super(1)B sub(2)) and the toluene cation (X super(2)B sub(1))

We commence by presenting an overview of the assignment of the vibrational frequencies of the toluene molecule in its ground (S0) state. The assignment given is in terms of a recently proposed nomenclature, which allows the ring-localized vibrations to be compared straightforwardly across different monosubstituted benzenes. The frequencies and assignments are based not only on a range of previous work, but also on calculated wavenumbers for both the fully hydrogenated (toluene-h8) and the deuterated-methyl group isotopologue ( alpha 3-toluene-d3), obtained from density functional theory (DFT), including artificial-isotope shifts. For the S1 state, one-colour resonance-enhanced multiphoton ionization (REMPI) spectroscopy was employed, with the vibrational assignments also being based on previous work and time-dependent density functional theory (TDDFT) calculated values; but also making use of the activity observed in two-colour zero kinetic energy (ZEKE) spectroscopy. The ZEKE experiments were carried out employing a (1 + 1') ionization scheme, using various vibrational levels of the S1 state with an energy