Interference of electric and magnetic dispersion forces between optically active and inactive molecules

Abstract

Angular momentum and irreducible tensor methods are used to derive the orientation dependence of the interaction energy between two molecules. Attention is given to the second-order energy resulting from the interference of electric and magnetic multipole interactions. Cases covered include (i) molecules with cylindrical interaction symmetry, (ii) one molecule rotating freely and the other fixed in orientation [see Eq.(16)], (iii) both molecules rotating freely [see Sec. IV, Eq. (19)], and (iv) both molecules fixed in orientation [see Eq. (15) and Eq. (22)]. Generalized expressions for the energy are obtained as matrix elements over contractions of irreducible spherical tensors. Explicit expressions, up through electric and magnetic octopole interference, are given. In the lowest order the expression for electric dipole and magnetic dipole interference agrees with the known expression derived by Craig, Power, and Thirunamachandran. New and higher order expressions derived here include interactions between one optically active molecule with another optically inactive molecule, plus interactions between two optically active molecules. Examples of the transformation properties of the multipole operators in the point group symmetry of the molecules are given. These are used to discuss the type of molecules which give rise to specific interactions and the resulting (angular) relationships between the transition multipoles of the two interacting molecules [Eq. (27)].