A simulation study of the vibration–rotational spectra of HCl diluted in Ar: Rotational dynamics and the origin of the Q-branch

A quantum stochastic simulation of the rotational motion of HCl molecules diluted in fluid Ar is presented at both sub-critical and supercritical temperatures. Simulated spectra are compared with the experimental data on the fundamental vibration–rotation IR band profiles for HCl in mixtures with dense Ar obtained at different thermodynamic states. Features of the observed triple PQR band structure are reproduced by simulations in a reasonable agreement with the experiment. A comparative study is made with the results of alternative classical molecular dynamics and classical stochastic simulations. The solute orientational relaxation, the relaxation time scales involved, the statistical properties of the nearest neighbor environment, and the nature of the central Q-branch are discussed.