Intermolecular vibrations of 1-naphthol•NH3 and d3-1-naphthol-ND3 in the S0 and S1 states

Hydrogen-bonded complexes of the photoacid 1-naphthol with NH3 and ND3 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 stretch <sigma>, the ammonia torsion tau, two in-plane wags beta (1) and beta (2), and two out-of-plane rocking motions 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 indicate 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 approximate to0.01 Angstrom upon S-1<--S-0 excitation, (C) 2001 American Institute of Physics.