Intermolecular vibrations of 1-naphthol·NH_3 and d_3-1-naphthol·ND_3 in the S_0 and S_1 states

摘要

Hydrogen-bonded complexes of the photoacid 1-naphthol with NH_3 and ND_3 were investigated by resonant two-photon ionization, spectral hole burning, and fluorescence spectroscopies. Although the intermolecular vibrations are weak in both absorption and emission, with typical Franck-Condon factors <2% relative to the electronic origin, all six intermolecular modes were identified, namely the hydrogen bond strength #sigma#, the ammonia torsion #tau#, two in-plane wags #beta#_1 and #beta#_2, and two out-of-plane rocking motions of #rho#_1 and #rho#_2. Several ammonia torsional excitations were observed, with spacings in good agreement with the S_0-and S_1 state effective torsional barriers derived by Humphrey and pratt [J.Chem. Phys. 104, 8332 (1996)]. The #beta#_1, #beta#_2, and #rho#_2 vibrational excitations exhibit large (2-8 cm~(-1)) torsional splittings, which indiate strong anharmonic coupling with the ammonia internal rotation. The observed Franck-Condon factors of the intermolecular stretching vibration imply a contraction of the O-H…N hydrogen bond by approx = 0.01 A upon S_1 <- S_0 excitation.