Vibrations and theoretical calculations of p-methylanisole in the first electronically excited S1 and ionic ground D0 states

One-color (1C), two-color (2C) resonant two-photon ionization (R2PI), and mass analyzed threshold ionization (MATI) methods have been applied to study the S1 ← S0 transition and threshold ionization of p-methylanisole. The excitation energy of the S1 ← S0 transition is determined to be 35,401 ± 2 cm−1, the adiabatic ionization energy of this molecule is measured to be 63,965 ± 15 and 63,972 ± 5 cm−1 by the 2C-R2PI and MATI methods. Most of the observed R2PI and MATI bands result from the in-plane ring vibrations. The frequencies of vibrations 9b, 1 and 7a are measured to be 393, 800 and 1168 cm−1 in the S1 state, and 412, 811 and 1220 cm−1 in the D0 state, respectively. This indicates the molecular structure in the D0 state is more rigid than that in the S1 state.