Stimulated Raman–UV Optical Double Resonance Spectroscopy of Van Der Waals Complexes of Benzene

Abstract

Spectroscopic and dynamical studies of the van der Waals complexes of benzene–Ar, benzene–N₂ and benzene dimer in the electronically ground state (S₀) have been performed by the use of stimulated Raman–UV optical double resonance spectroscopy. The vibrational frequency of mode 1 of the complexes and the decay rate constants of the 1₁ levels (∼993 cm^-1) have been measured. The vibrational frequency shifts of mode 1 in S₀ upon complex formation were less than 1 cm^-1for all the complexes. On the other hand, the decay rate constant due to intramolecular vibrational redistribution and/or vibrational predissociation showed a drastic change. The decay rate constant of the 1₁ level of the benzene dimer was 2.4 × 10⁷ s^-1, while those of the benzene–Ar and benzene–N₂ complexes were much smaller than 1 × 10⁶ s^-1. It was also found that the decay rate constant in S₀ is much smaller than that in S₁. For the benzene dimer, the depolarization ratio of Raman band of mode 1 was recalculated by taking into account of the anisotropy of the polarizability of benzene molecule. The comparison between the observed and calculated polarization ratio shows that the benzene dimer has the “T-shaped” structure which was proposed by the group of Felker.