Angular correlations and rotational motion in computer-simulated liquid nitrogen

Abstract

Further results of a "molecular dynamics" simulation of liquid nitrogen are described. These results have been obtained under triple-point conditions. A molecular-pair distribution function which depends on the radial distance, plus three angular variables, has been computed. Partial averages of this function are depicted. These functions show an angular structure up to about 9 \AA{}, but are not sharply peaked. It seems that the orientation of a molecule is more influenced by the positions of its neighbors than by their orientations. The dynamics of the orientational motion has also been further studied. The coupling between the environment and the orientational behavior of a given molecule has been examined through both cross-correlation functions and selectively sampled correlation functions. These results are the following: (i) An initial high rotational temperature of the molecule facilitates its reorientation. (ii) An initial fluctuation of the local density affects the reorientational behavior of the molecule only if this fluctuation persists for a sufficiently long time. (iii) By contrast, there is little coupling between the behavior of a molecule and the rotational temperature of its interacting partners. (iv) Individual samples of the motion indicate that a molecule shares its time about equally between periods of orientational trapping, with erratic librational motion, and periods of continuous nonuniform rotation.