Mass analyzed threshold ionization spectroscopy of methyl-p-aminobenzoate cation

The adiabatic ionization energy of methyl-p-aminobenzoate has been determined to be 63549 ± 5 cm−1, which is greater than that of aniline by 1278 cm−1. This blue shift results from the COOCH3 substitution at the para position and is consistent with that predicted by the Gaussian-3 calculations. Analysis on the cation spectra shows that the active vibrations include in-plane modes 9b, 6b, 12 and 1 with frequencies of 476, 599, 803, and 831 cm−1, respectively.