Cartesian coordinates, vibration-rotation Hamiltonians

One of the important ingredients to being able to use CVPT to study molecular vibrations and rotation-vibration interactions is the expansion of the Hamiltonian. In our work, we follow the work of Pickett (63) and use very general expressions for the terms in the Hamiltonian. The evaluation of these terms requires simply the ability to convert from Cartesian to internal coordinates and back to Cartesian coordinates. Given an expansion of the Hamiltonian, about the potential minimum, in some appropriate set of coordinates, CVPT can be applied to this Hamiltonian in a straightforward manner. This is one of the advantages of this approach. The actual transformations required to obtain the effective Hamiltonian are independent of the details of the molecular Hamiltonian. 

The center of mass translational energy may be removed from in eqn (20.26) to give a Hamiltonian for vibrational/rotational motion, which may be expressed in Cartesian, internal or normal mode coordinates. The... 

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