Subject: CCL: TD-DFT singlets vs triplets intensity

From: Steve Williams <willsd ## appstate.edu>
Date: Fri, 20 May 2005 16:22:16 -0400

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