Quantum dynamics of non - rigid systems comprising two polyatomic fragments

We combine earlier treatments for the embedding of body-fixed coordinates in linear molecules with the close-coupling formalism developed for atomdiatom scattering and derive a hamiltonian which is most convenient for describing the nuclear motions in van der Waals complexes and other non-rigid systems comprising two polyatomic fragments, .4 and B. This hamiltonian can still be partitioned in the form I~A + I2IB + I~INT, just as the space-fixed hamiltonian. The body-fixed form, however, has several advantages. We discuss solution strategies for the rovibrational problem in non-rigid dimers, based on this partitioning of the hamiltonian. Finally, in view of the size of the general polyatomic-polyatomic case, we suggest problems which should be currently practicable.