Vibration—rotation spectra of CO in liquid alkanes

Vibration—rotation infrared spectra have been obtained for CO dissolved in a variety of branched and normal alkanes. The normalized band profiles yield rotational correlation functions, correlation times and the torques acting on the CO molecule. These quantities and the band shape depend only on the alkane free volume, contrasting with the situation for DC1 solute where they showed a strong dependence on solvent molecular shape. The Gordon m-diffusion model for rotational diffusion gives good predictions for the correlation functions and a complete fit is obtained using the generalized m-diffusion model incorporating a small frequency-dependence of the effectiveness of a collision in changing the rotor angular momentum. This success of simple stochastic theory contrasts with its failure for DCl in these alkanes.