Geometry and vibrations of N-methylpyrrole in the S0 state studied by dispersed fluorescence spectroscopy and ab initio calculations

A number of vibrational frequencies in the ground state of N-methylpyrrole (C4H4NCH3) have been determined via laser-induced dispersed fluorescence spectra recorded under jet-cooled conditions. Eight vibronic levels of the symmetry forbidden 3s(A(2))S-1 <-- (A(1))S-0 Rydberg transition were pumped including the methyl rotor levels 2e', 3+, 3- and 4e'. The DF spectra provided a detailed look of the S-1-S-0 inducing modes. The geometrical structure and the vibrational modes of NMP in the So electronic state have been calculated at the DFT and MP2 level using two basis sets, 6-311G** and D95++. The barrier for the methyl group rotation is also calculated. (C) 2003 Elsevier Science B.V. All rights reserved.