The vibronically-resolved emission spectrum of disulfur monoxide (S2O):: An algebraic calculation and quantitative interpretation of Franck-Condon transition intensities

Emission spectra obtained from jet-cooled disulfur monoxide (S2O) molecules have been interpreted by means of a novel Lie algebraic formalism that makes possible the facile evaluation of multidimensional Franck-Condon factors. Fluorescence accompanying selective excitation of isolated vibronic bands in the S2O (C) over tilde (1)A(')<--(X) over tilde (1)A(')(pi(*)<--pi) absorption system has been dispersed under moderate spectral resolution, allowing assignment of ground state levels possessing up to 20 quanta of vibration in the nu(2) S-S stretching mode [E-vib((X) over tilde)less than or equal to 13 900 cm(-1)]. Aside from providing a rigorous and economical description for the inherently anharmonic nature of highly-excited polyatomic species, our algebraic approach enables quantitative information on molecular wavefunctions to be extracted directly from spectroscopic data. The emerging picture of S2O vibrational dynamics suggests that the X (1)A(') potential surface is substantially more "local" in character than the C (1)A(') manifold. While the observed pattern of X (1)A(') vibrational energies could be reproduced well through use of model Hamiltonians that include only diagonal anharmonicities in the local algebraic basis, successful treatment of the C (1)A(') state necessitated explicit incorporation of off-diagonal anharmonicities that lead to pervasive mixing of local vibrational character. This disparate behavior is manifest strongly in measured C-X transition strengths, thereby allowing detailed investigations of Franck-Condon intensities to discern the underlying dynamics. Structural parameters deduced from algebraic analyses are in good accord with previous predictions of the change in S2O geometry accompanying pi(*)<--pi excitation. (C) 1999 American Institute of Physics. [S0021-9606(99)00635-2].