Local coherence in the orientational dynamics of highly polar liquids

For the three liquid methylhalides, CHF3, CH3F, and CH3Cl, we describe a correlation function analysis of the rotational motion, extended over all the liquid-gas coexistent states. These orientational correlation functions are exponential at long times and damped oscillatory at short times. Experimental memory functions are computed, and a comparison with the rotational velocity correlation functions show generally acceptable agreement. The nature of the microscopic motion in the frame of either Cole-Glarum or Fatuzzo-Mason theories is compared, indicating generally weak deviations. Some examples are presented of the amplitudes of mean squared torques and their variations under orthobaric conditions. The physical situation in fluoroform is further analysed with the help of τ1/τ2 ratios, indicating that in this liquid a satisfactory description is gained with the itinerant oscillator model. Finally, the validity of the collisional models under their various formulations is shown to be, at the least, dubious.