A vibrational analysis for the excitation and fluorescence spectra of the S1–S0 transition in jet-cooled indole and N-deuterated indole is presented. This analysis yields the frequencies for eight low-lying S1 vibrational modes of both isotopic species. Single vibronic level fluorescence spectra also enable us to refine many of the S0 vibrational frequencies. Quantum interference effects in the energy-resolved fluorescence decays for one vibrational level of S1 indole are observed as a result of picosecond laser excitation. Through analysis of the fluorescence spectra and the modulated fluorescence decays, the coupling responsible for the quantum beats was found to result from a zero-order in-plane mode coupled to a level which is described by several zero-order out-of-plane modes. The effect of the deuterium substitution on the quantum beats is also investigated.

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The excited state dynamics of the indole(Ar)1, indole(d1)(Ar)1, indole(Ar)2, and indole(CH4)1 van der Waals clusters have been investigated in a free jet expansion. Excited state vibrational frequencies were determined using multiphoton ionization and fluorescence excitation spectroscopy. Time resolved emission spectroscopic techniques were used to determine vibrational predissociation rates and product state distributions. All of the clusters were found to predissociate when excited with sufficient vibrational energy in the S1 state. The predissociation dynamics were found to be consistent with a serial model in which energy transfer from the indole skeletal modes to the van der Waals modes precedes the dissociation step. The density of van der Waals vibrational states was found to be the most important factor in determining the predissociation dynamics.

!his paper, last in this series, reports on the picosecond dynamics of vibrational predissociation In beam-cooled van der Waals' clusters. Reaction rates have been measured for clusters (1: 1) of phenol and cresol (p-methylphenol) with benzene by the picosecond pump-probe photoionization mass-spectrometry technique. Dissociation to form phenol (cresol) and benzene takes place from vibrational levels of the S) state of phenol (cresol) prepared by the pump laser. The predissociation rates were measured for a number of different excess energies upto-2500 cm-), and the reaction threshold was found to be 1400 cm-) above the S) origin for phenol-benzene and-1795 cm-) for cresol-benzene, respectively. For phenol-benzene, the predissociation rates, following excitation of ring-type modes, vs excess energy vary more or less smoothly. Cresol-benzene exhibits biexponential decay, with the fast component becoming more dominant at higher energies. A non-RRKM model involving division of the vibrational phase space is discussed to explain this observation.

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