Spectroscopic manifestation of molecular rotation dynamics in dense media: CO fundamental band in liquid and solid CO-Kr and CO-Xe solutions

Abstract

Abstract The shape of the CO fundamental band has been studied in CO-Kr and CO-Xe mixtures in a wide temperature range from the critical temperature to values lower than the melting point of the solutions. The band shape transformation has been analyzed by means of a simple cell model, which takes into account the effect of the nearest environment on CO rotation dynamics of a molecule in dense media. The band shape observed in liquid solutions shows the constraint of CO rotational mobility; this effect has been described by introducing an effective potential barrier for rotational motion. The model analysis of the obtained experimental data results in an estimation of the rotational motion relaxation parameter and of the effective barrier values for CO dissolved in Kr and Xe. The CO rotational motion becomes more hindered when going to lower-temperature liquid solutions. The liquid-to-solid phase transition leads to an increase of the relaxation rate, the effective barrier values decrease, and the rotational motion tends to become rotational diffusion.