Mass analyzed threshold ionization spectroscopy of p-methoxyaniline cation and influence of the OCH3 substituent

We report the mass analyzed threshold ionization (MATI) spectra of p-methoxyaniline recorded via the 00 vibrationless and several vibrational levels in the S1 state. The adiabatic ionization energies (IE) of this molecule is determined to be 57 445±5 cm−1, which is red shifted from that of aniline by about 4826 cm−1. This large energy shift is attributed by the electron-donating nature of the OCH3 group, supported by the ab initio calculations. In addition, the presence of the methoxy substituent also influences the vibrational frequencies depending upon the pattern.