Mass selected resonance enhanced multiphoton ionization spectroscopy of aniline–Arn (n=3,4,5, ...) van der Waals complexes

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Abstract
The origin region of the S1←S0 transitions of the aniline–Ar3, aniline–Ar44, and aniline–Ar5 molecules have been measured using mass selected resonance enhanced, multiphoton ionization (REMPI) spectroscopy. The aniline–Ar3 spectrum exhibits two distinct groups of peaks. The more prominent group displays a regular vibrational progression, with five obvious members and a spacing of ∼16 cm−1. Vibrational structure in the other group is less distinctive. On the basis of cluster potential calculations described in this paper, we believe that two stable aniline–(argon)3 isomers exist in the supersonic expansion and that the two groups of peaks correspond to absorption by these two isomers. Spectra recorded at masses corresponding to aniline–(argon)4 and aniline–(argon)5 display broadened structure that probably reflects contributions from larger aniline–(argon)n clusters which fragment upon ionization. There is, however, some evidence for a progression with a spacing of ∼16 cm−1 in the aniline–(argon)4 spectrum. Dispersed fluorescence spectra from relatively small aniline–Arn clusters (4<n<10) indicate that vibrational redistribution from Franck–Condon active van der Waals modes occurs with rates of at least 5×109 s−1.