Abstract

The SEP–LIF (stimulated emission pumping-laser induced fluorescence) technique was applied to the investigation of dynamical behavior of vibrationally excited phenol and anisole produced in the supersonic expansion. In the SEP–LIF scheme, a molecule excited to a specific vibrational state by SEP is detected by measuring the LIF excitation spectrum with an appropriate delay to probe the vibrational relaxation. Four vibrational states, 6a₁, 16a₂, 12₁ and 1₁, of phenol, and six vibrational states, 18b₁, 18b₂, 6a₁, 12₁, 16a₂ and 1₁, of anisole were investigated. For both of phenol and anisole, it is found that the relaxation of the vibrational states below 1,000 cm^-1 in the ground electronic state is so slow under the collisionless condition that only the transitions from the vibrational states initially prepared by SEP are observed as the SEP-induced bands in the SEP–LIF spectra. The low frequency torsional motion of methyl group in anisole does not accelerate IVR (intramolecular vibrational redistribution) much in this energy region.