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

The shape of the CO fundamental band has been studied in CO-Kr and CO-Xe mi xtures in a wide temperature range from the critical temperature to values lower than the melting point of the solutions. The band shape transformatio n has been analyzed by means of a simple cell model, which takes into accou nt the effect of the nearest environment on CO rotation dynamics of a molec ule in dense media. The band shape observed in liquid solutions shows the c onstraint of CO rotational mobility, this effect has been described by intr oducing an effective potential barrier for rotational motion. The model ana lysis of the obtained experimental data results in an estimation of the rot ational 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 barr ier values decrease, and the rotational motion tends to become rotational d iffusion. (C) 2001 Elsevier Science B.V. All rights reserved.