Atom-pair formulation of the rotational and vibrational motions of molecules

We have expressed the angular momentum and the internal kinetic energy of a molecule (a system of point masses) in terms of atom-pair contributions, p aralleling the use of pairwise additive potential energy functions. The par titioning of the internal kinetic energy into rotational and vibrational co ntributions is then made following the analysis of Jellinek, J., and Li, D. H., 1989, Phys. Rev. Lett., 62, 241. The resulting expressions contain pai r position and velocity variables whose redundancy may be removed by transf ormation to Jacobi vector coordinates. These expressions should prove espec ially useful for describing the internal motions of clusters of like atoms.