COMPUTERIZED SIMULATION AND FITTING OF SINGLET-TRIPLET SPECTRA OF ORTHORHOMBIC ASYMMETRIC TOPS - THEORY AND EXTENSIONS TO MOLECULES WITH LARGE MULTIPLET SPLITTINGS

Motivated by our recent finding that the singlet-triplet bands of sele noformaldehyde involve an upper state with large zero field splittings , we have extended the theory and written a program for predicting and fitting such rotationally resolved spectra. Triplet state matrix elem ents for a case (A) basis have been developed; including corrections f or centrifugal and spin-centrifugal distortion. The full Hamiltonian m atrix has been symmetry adapted, simplifying the problem to four indiv idual matrices of approximately equal size for molecules of orthorhomb ic symmetry. Diagonalization of these matrices yields triplet state en ergies that are in agreement with previous treatments using a basis in which the spin splittings are small relative to the rotational interv als. Methods have been developed for sorting the eigenvalues and assig ning quantum labels regardless of the magnitude of the spin splittings . The calculation of the relative intensities of the rotational lines, within a band has been programmed using transition moment matrix elem ents from the literature. The selection rules for various upper state symmetries have been developed in a form useful for the analysis of sp ectra. Band contour predictions of spectra for various coupling cases have been presented. (C) 1995 American Institute of Physics.