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Fluorescence excitation and dispersed fluorescence spectra of jet-cooled naphthalene and 2,6-, 2,7-dimethylnaphthalenes have been measured. The frequencies of optical active vibrations in the ground and first excited singlet states have been determined. The new technique for calculation of planar vibration frequencies of polycyclic benzenoid hydrocarbons in the excited electronic states has been developed. The vibration frequencies in the ground and first excited singlet states of these molecules were calculated using the developed technique and the Ohno's model. The interpretation of vibronic spectral lines based on the comparison of the calculated and experimental data was made. The calculation rms errors for the vibration frequencies in the ground electronic states of the investigated molecules do not exceed 20 cm-' and are approximately 1.5 times higher for excited states without additional adjustment of parameters for individual molecules.

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It was established analytically that the results of measurements of the excited-state lifetime of dye molecules using bleaching curves of solutions are influenced by the polarization of the radiation, the anisotropy of the molecular absorption and emission oscillators, and the rotational diffusion time of the molecules. These factors could alter almost twofold the ratio of the molecular lifetime to the observed bleaching intensity of the solution. A 300-ps neodymium laser pulse was used to obtain bleaching curves of various dye solutions and to determine the lifetimes of these dyes in the 2.5-130 ps range. The results of measurements on a solution of dye No. 15 led to its testing as a passive switch in a neodymium-doped lanthanum beryllate laser and its potential for mode locking of neodymium laser radiation was demonstrated.