MANY-BODY CORRELATIONS IN MULTIPOLE-INDUCED DIPOLE ABSORPTION-SPECTRAOF LIQUID OCS

Time correlation functions for several multipole-induced dipole moment s corresponding to absorption in the far-infrared spectral region have been evaluated from molecular dynamics computer simulations of liquid carbonyl sulfide (OCS). Five state points along the liquid-vapor coex istence curve have been investigated. The dipole-, quadrupole- and oct opole-induced dipole moments have been estimated for the interacting p airs of molecules in the liquid. The induced moments are produced by t he action of the electric fields of the molecular electrostatic multip oles upon the anisotropic polarizabilities of the OCS. The component n -body (n = 2,3,4) time correlation functions for these multipole-induc ed dipole moments as well as those for the cross-correlation functions between the induced and the permanent dipole moments of these molecul es have been calculated. It is shown that the n-body terms involved in the time correlation functions containing quadrupole-induced dipole m oments cancel each other at long times. Furthermore, 4-body correlatio ns are significantly less important than the 2- and 3-body contributio ns for all induction mechanisms investigated here. (C) 1997 Elsevier S cience B.V.