Intermolecular forces and orientational phase transitions in molecular crystals

Abstract

The conditions under which one expects orientational phase transitions are discussed in the introduction. Then we consider the interactions between molecules and construct a Hamiltonian which is compared with the spin Hamiltonians that are in common use in the field of critical phenomena. A definition of the order parameter is given with special attention to the ordering of higher multipoles and with a discussion of its experimental determination. Finally the opportunities of obtaining information about critical exponents are considered, but the prospect is rather unpromising.