Energy relaxation of N2O in gaseous, supercritical, and liquid xenon and SF6

Rotational and vibrational energy relaxation (RER and VER) of N2O embedded in xenon and SF6 environments ranging from the gas phase to the liquid, including the supercritical regime, is studied at a molecular level. Calibrated intermolecular interactions from high-level electronic structure calculations, validated against experiments for the pure solvents, were used to carry out classical molecular dynamics simulations corresponding to experimental state points for near-critical isotherms. The computed RER rates in low-density solvents of krotXe=(3.67±0.25)×1010 s-1 M-1 and krotSF6=(1.25±0.12)×1011 s-1 M-1 compare well with the rates determined by the analysis of two-dimensional infrared experiments. Simulations find that an isolated binary collision description is successful up to solvent concentrations of ∼4 M. For higher densities, including the supercritical regime, the simulations do not correctly describe RER, probably due to the neglect of solvent-solute coupling in the analysis of the rotational motion. For VER, the near-quantitative agreement between simulations and pump-probe experiments captures the solvent density-dependent trends.