THE VANDERWAALS VIBRATIONS OF ANILINE (ARGON)2 IN THE S1 ELECTRONIC STATE

Vibrational structure associated with van der Waals modes of the aniline-(argon)2 complex has been observed in the region near the origin of the S1 <-- S0 electronic transition of the complex using resonance enhanced, multiphoton ionization (REMPI) spectroscopy. The aniline-Ar2 spectrum in this region displays only a few discrete bands built on an intense electronic origin. The dominant vibrational band, associated principally with the symmetric van der Waals stretching motion of the two argon atoms against the aromatic frame, occurs at 38.5 cm-1 displacement relative to the 0(0)0 band, with weaker transitions at 15 and 30 cm-1 displacement. A simple model for the van der Waals vibrations of aromatics bound to one and two rare gas atoms is developed and allows allow us to explain the aniline-Ar2 spectrum, using van der Waals bond parameters determined from the previously measured An-Ar1 spectrum. The agreement between the predicted and observed aniline-Ar2 spectrum confirms the view that van der Waals stretching vibrations are coupled anharmonically to near resonant bending vibrations in aniline-Ar1 and aniline-Ar2.