The rovibrational kinetic energy for complexes of rigid molecules

The rovibrational kinetic energy for an arbitrary number of rigid molecules is computed. The result has the same general form as the kinetic energy in the molecular rovibrational Hamiltonian, although certain quantities are a ugmented to account for the rotational energy of the monomers. No specific choices of internal coordinates or body frame are made in order to accommod ate the large variety of such conventions. However, special attention is pa id to how key quantities transform when these conventions are changed. An e xample system is analysed explicitly as an illustration of the formalism.