Quantum yield of photochemical reactions

[Arvydas Tamulis <tamulis:at:mserv.itpa.lt>]

 Dear Colleagues,
Would you please to say how to calculate quantum yield of
 photochemical
 reactions using resulting files of Gaussian03 or GAMESS-US
 calculations.
 Or maybe you can offer other possible evaluations of quantum yield of
 photochemical reactions.
 Best regards,
 Arvydas Tamulis
 www.itpa.lt/~tamulis/