Jet spectroscopy of van der Waals dimers of 1-methoxynaphthalene: A laser induced fluorescence study

Excited state dynamics following S-1<--S-0 transition of jet-cooled van der Waals complexes of 1-methoxynaphthalene has been investigated by measuring the laser-induced fluorescence excitation, dispersed fluorescence and two-color hole-burning spectra. The results give evidence of formation of two isomeric dimers, which show only sharp absorption and emit excimer fluorescence for excitations to the origin region of the S-1 state. Excimer formation in one of the dimers occurs from the zero-point level of the locally excited state. The other dimer shows vibrational barrier and the yield of the excimer emission increases as the successive higher quanta of a low-frequency intermolecular mode are excited. The barrier in the second case has been attributed to the reorganization of the dimer geometry from the locally excited state to the excimer state. The characteristic enhancement of the yield of excimer emission with increase in excitation energy indicates the involvement of a tunneling mechanism for crossing the reorganization barrier. (C) 2001 American Institute of Physics.