Two-color resonance enhanced two-photon ionization and mass analyzed threshold ionization spectroscopy of 2-methoxybenzonitrile

Abstract We report the two-color resonance enhanced two-photon ionization (R2PI) and mass analyzed threshold ionization (MATI) spectra of 2-methoxybenzonitrile. The origin band of S1 ← S0 transition and accurate adiabatic ionization energy of 2-methoxybenzonitrile are determined to be 34,176 ± 2, and 70,658 ± 5 cm-1, respectively. The Franck-Condon simulations of the vibrationally resolved electronic spectra for S1 ← S0 and D0 ← S1 transitions are calculated and used to assist the assignments of the vibronic bands in the experimental spectra. The active vibrations in the S1 and D0 states are mainly associated with the motions of the in-plane ring deformation and the in-plane ring-OCH3 bending. A propensity rule of Δ υ = 0 , observed in the MATI spectra recorded via different intermediate states, suggests that the molecular geometry of 2-methoxybenzonitrile in the D0 state resembles that in the S1 state. Comparing the transition energies of 2-methoxybenzonitrile with those of anisole, benzonitrile and ortho substituted derivatives provides insight into the substitution effect of CN and OCH3 groups on the transition energies.