A GENERAL PROGRAM FOR THE CALCULATION OF INTERNAL ROTATION SPLITTINGS IN MICROWAVE SPECTROSCOPY.

A theoretical basis is presented for a computer program which has been written to calculate the internal rotation splittings in the microwave spectra of molecules possessing a hindered internal symmetric top. This is an extension of the internal axis method and is applicable to a very general case, which includes any high barrier problem which is not a near spherical top. Any asymmetry, any geometry, and any size top can be handled by the program as it stands. The method involves the division of the Hamiltonian into a rotational part and a part involving internal rotation, the latter including the coupling between internal and overall rotation. The matrix elements of these parts are set up separately, each in the most convenient basis, then transformed to a common basis symmetric rotor in principal axes, then to the Wang basis, and finally to the basis which diagonalizes the large rigid rotor part. The small off-diagonal elements which are left are treated by perturbation theory. This procedure has been incorporated in an efficient Fortran program which uses fully the various symmetry properties. Author