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In order to aid in the development of computational methods to guide environmental chemistry, methods for estimating triplet quantum yield (TQY) were applied to 3 test molecules: benzene, aniline and acetophenone. The Landau-Zener model was implemented with an Arrhenius type rate equation to determine relative intersystem crossing (ISC) and internal conversion (IC) rates. Preliminary calculations using this approach considering only the S0, S1and T1 states gave estimates of TQY at 0.56 for aniline (experimental: 0.9)2 and 1.00 for benzene (experimental 0.15).2 Although this estimate for aniline was deemed within acceptable range for predictive purposes, the estimate for benzene incorrectly estimated IC rate to be negligible relative to ISC rate. Due to long calculation times for the calculations required for the Landau-Zener model, as well as its unreliable predictions in this implementation, a second method was pursued using Fermi’s Golden Rule (FGR). TQY predictions were not obtained for the test molecules with the FGR method due to insufficient memory and computational speed to handle all of the Franck-Condon factors (FCFs) involved in the calculation. Recursive selection criteria were implemented for removing negligible FCFs, but the criteria implemented were insufficient for properly eliminating terms, and it was determined that more sophisticated selection criteria were necessary for effective implementation of FGR in this application.
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