PHYS 10 |
| In recent years ab initio electronic structure calculations of electronic circular dichroism spectra have advanced significantly. Comparison with experiment, even in the gas phase, is still hampered, however, by a lack of consideration of vibrational fine structure in most calculations today. The various electronic states contributing to a CD spectrum can have very different vibrational fine structure, leading to either sharp and distinct, or diffuse and not easily recognizable, contributions to the overall CD spectrum. In this presentation it is discussed how a general vibronic model, suitable for faithful simulations of CD spectra, can be obtained from present-day electronic structure calculations. The vibronic model serves as the basis for various simulations of the CD spectra. Franck-Condon calculations are the simplest and provide reasonable agreement with experiment for test cases considered, in particular dimethyloxirane. The intensities in FC simulations can be somewhat off however, as the magnetic and electric transition dipole surfaces tend to have significant variation due to the mixing of electronic states that have overall rotary strengths of different sign, as a function of nuclear geometry. The quality of the simulations can be improved by computationally expensive simulations that fully incorporate effects from non-adiabatic dynamics, but alternatively, the above Herzberg-Teller type of effects can be simulated very effectively by classical simulations to obtain effective rotary strenghts, which can then be used in a conventional Franck-Condon calculation. |
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Implications and Applications of Chirality in Physical Chemistry
8:00 AM-12:00 PM, Sunday, March 25, 2007 McCormick Place South -- Room S401A, Level 4, Oral
Division of Physical Chemistry |