First vibrational overtone bandshape of HCl in fluid SF6: An experimental and theoretical study

Abstract

The first overtone band profiles are recorded in the IR spectra of the HCl molecular probes diluted in SF₆, both below and above the critical point of the solvent. The spectral density distribution is considered as an additive superposition of the contributions due to the quasifree rotating and the rotationally-hindered probes. A recently proposed spectral theory is applied for description of the quasifree contribution. Good agreement is obtained between the experimental and calculated spectral profiles. The vibration–rotation coupling constant for the HCl molecules is found to decrease in high-density fluids. The central Q-branch components associated with the hindered solute states are separated from the measured spectra and their transformation is studied in a broad range of well-controlled thermodynamic conditions. We discuss the possible influence of the interaction-induced dipole transitions on the absorption in the vicinity of the band center.