STRUCTURES AND VIBRATIONS OF P-METHYLANILINE IN THE S-0 AND S-1 STATES STUDIED BY AB-INITIO CALCULATIONS AND RESONANT 2-PHOTON IONIZATION SPECTROSCOPY

The structures and normal vibrations of p-methylaniline (pMA) in both the S-0 and S-1 states have been studied using ab initio quantum chemi cal calculations and resonant two-photon ionization (R2PI) spectroscop y. Calculated results at MP2/6-311+G* and CIS-MP2/6-311+G** levels sh ow that the minimum energy conformations of pMA in both states have a hydrogen atom of the methyl group perpendicular to the plane of the ri ng. In the S-1 state, the molecule contracts along the in-plane long a xis and the C-N bond exhibits a partial double bond character due to l arger pi-electron conjugation as in the case of aniline, A comparison of the calculated excited and ground state vibrational frequencies has made it possible for us to successfully assign our measured R2PI spec tral bands as well as the previously reported ground state features. ( C) 1998 Elsevier Science B.V.