FLUORESCENCE-DIP AND STIMULATED-EMISSION-PUMPING LASER-INDUCED-FLUORESCENCE SPECTRA OF VANDERWAALS MOLECULES CONTAINING BENZONITRILE

Fluorescence-dip spectra of benzonitrile and some van der Waals complexes containing benzonitrile (benzonitrile dimers, benzonitrile-Ar, and benzonitrile-H20) were measured. The vibrational bandwidths in the fluorescence-dip spectra were found to be determined by the rotational structure and not by the rate of vibrational dissociation of the complex or by the rate of vibrational relaxation into the intermolecular modes. Stimulated-emission-pumping (SEP) laser-induced-fluorescence (LIF) spectra were also measured to permit the study of the dynamical behavior of the complexes. The relaxation of the vibrational states (v10, V12, and V10 ± v12 of benzonitrile) prepared by SEP was probed directly by varying the delay between the SEP andLIF laser pulses. The monomer showed slow decay, which could be due to the escape of the vibrationally excited species out of the probe region. On the other hand, the dimer showed no detectable LIF signal, indicating fast relaxation of the prepared vibrationally excited state. Finite decay rates were obtained for benzonitrile-Ar and benzonitrile-H 20, which were not sensitive to the vibrational energy. Some advantages of using the fluorescence-dip and SEP-LIF techniques in the study of vibrational spectroscopy and the dynamics of van der Waals complexes are pointed out and discussed. © 1990 Optical Society of America.