CCL: TD-DFT singlets vs triplets intensity

[Steve Williams <willsd ## appstate.edu>]

 I have carried out some TD-DFT calculations in G03 on two rather large
 (about 150 atoms) molecules that each have a single Re atom in the
 center
 of the molecule.  For each I have 50 singlet and 50 triplet states; the
 molecular ground state is a singlet (nice sharp NMR spectra).  Of
 course
 G03 gives oscillator strengths of zero for each triplet excitation,
 since
 the calculation does not use spin-orbit effects.  With a heavy atom
 like
 Re, the spin orbit coupling will be large, and this will likely cause
 the
 triplet excitations to contribute to the observed spectrum.  I have
 thought
 about looking at each of the orbitals involved in each excitation and
 identifying those that have some contribution from the Re atom.  I
 think
 the excitations involving these should make some contribution to the
 absorbance spectrum.  Does anyone have any suggestions about how to
 estimate (even crudely) the oscillator strengths of these excitations?
 Thanks,
 Steve
 Steve Williams
 A. R. Smith Department of Chemistry
 Appalachian State University
 Boone, NC 28608
 USA
 828-262-2965