Resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of the selected rotamers of m-methoxyaniline and o-methoxyaniline

We report the resonant two-photon ionization and mass-analyzed threshold ionization (MATI) spectra of m-methoxyaniline and o-methoxyaniline. The vibronic features of m-methoxyaniline are built on 34308 ± 2 and 34495 ± 2 cm−1 corresponding to the origins of the S1 ← S0 electronic transition (E1's) of the cis and trans rotamers. Analysis of the MATI spectra gives the adiabatic ionization energies (IEs) of 59983 ± 5 and 60879 ± 5 cm−1 for these two species. o-Methoxyaniline is found to have only one stable structure whose E1 and IE are 33875 ± 2 and 58678 ± 5 cm−1, respectively. Most of the active vibrations of m- and o-methoxyaniline in the electronically excited S1 and cationic ground D0 states result from the in-plane ring vibrations. Comparing these data with those of p-methoxyaniline allows us to learn about the vicinal substitution effects resulting from the relative locations of the NH2 and OCH3 substituents.