MASS SELECTED RESONANCE ENHANCED MULTIPHOTON IONIZATION SPECTROSCOPY OF ANILINE-ARN (N=3,4,5,...) VANDERWAALS COMPLEXES

The origin region of the S1 <-- S0 transitions of the aniline-Ar3, aniline-Ar4, 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 approximately 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 approximately 16 cm-1 in the aniline-(argon)4 spectrum. Dispersed fluorescence spectra from relatively small aniline-Ar(n) clusters (4 < n < 10) indicate that vibrational redistribution from Franck-Condon active van der Waals modes occurs with rates of at least 5 x 10(9)s-1.