Vibrational energy relaxation of azulene studied by the transient grating method. I. Supercritical fluids

The vibrational energy dissipation process of the ground-state azulenein supercritical xenon, carbon dioxide, and ethane has been studied by the transient grating spectroscopy. In this method, azulenein these fluids was photoexcitedby two counterpropagating subpicosecond laser pulses at 570nm, which created a sinusoidal pattern of vibrationally hot ground-state azuleneinside the fluids. The photoacoustic signal produced by the temperature rise of the solvent due to the vibrational energy relaxationof azulenewas monitored by the diffraction of a probe pulse. The temperature- rise timeconstants of the solvents were determined at 383 and 298K from 0.7 to 2.4 in ρr, where ρr is the reduced density by the critical density of the fluids, by the fitting of the acoustic signal based on a theoretical model equation. In xenon, the temperature- rise timeconstant was almost similar to the vibrational energy-relaxation time constantof the photoexcitedsolute determined by the transient absorption measurement [D...