Cross-orientational motion in liquid dichloromethane and trichloromethane (chloroform) by molecular dynamics simulation

Abstract

Using molecular dynamics the l = 1 orientational auto- and cross-correlation functions of one of the C–H bond directions of neat dichloromethane at 273 K and that of chloroform between 301 and 438 K in its neat state and in solution with tetrachloromethane and liquefied methane (at 183 K) have been simulated. The simulations are confined to a model of singly rotating, individual molecules in the absence of induced absorption and translation-rotation coupling. It is found throughout that the orientational cross-correlation functions are equivalent to the auto-correlation functions, therefore bearing the same information content. On the basis of a simple thermodynamic argument, this phenomenon is extended to be generally valid to orientational correlation functions from vibration–rotation spectra of mobile liquids. Consequences of the equivalence are, first, that dilution does not break the symmetry between orientational auto- and cross-correlation functions of the solute species and, second, that the simulated auto-correlation functions of total and individual dipole moments of undressed dipoles in the system are indistinguishable.