Symmetry effects of electric and magnetic fields in liquid state molecular dynamics

It Is shown that ensemble averages in molecular liquids may be investigated using group theoretical methods. These my he applied both in the laboratory frame (X,Y,Z) and the frame of the principal molecular moments of inertia (x,y,z). Using these methods the effect of an external electric field () and external magnetic field () may be considered in terms of second order quantities such as the single molecule cross correlation function (t)^T(o) where is the molecular centre of mass linear velocity and the angular velocity of the same molecule. Group theory, applied in this way, confirms the recent discovery by computer simulation of non-vanishing elements of (t)^T(o) in frame (X,Y,Z) in the presence of an electric field. Group theory predicts, however, that these elements vanish in the presence of a magnetic field, even though this produces alignment and birefringence through the Langevin function. This leads to a straightforward experimental method for the direct observation of the non-vanishing elements of (t)^T(o).