Terahertz absorption spectra of supercritical CHF3 to investigate local structure through rotational and hindered rotational motions

Far infrared absorption spectra of neat supercritical fluoroform (CHF3) are measured with terahertz (THz) radiation. The spectra covering from 10 to 1 00 cm(-1) are obtained at reduced temperature T/T-c = 1.02 on densities var ied by a factor of 200. As density increases, dominant component of spectra changes from rotational to hindered-rotational motions. However, the chang e is nonlinear to the density. Such specificity arises from difference betw een bulk and local densities, and the most enhanced local density is observ ed near the thermodynamic state of maximum density fluctuation. In the pure fluid system, the relationship between density fluctuation and local densi ty enhancement is experimentally presented. (C) 2001 Elsevier Science B.V. All rights reserved.