Mixed quantum/semiclassical wave-packet dynamical method for condensed-phase molecular spectroscopy signals
| Autor: | Philip A. Kovac, Jeffrey A. Cina |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
Physics
010304 chemical physics Absorption spectroscopy Wave packet Gaussian Degrees of freedom (physics and chemistry) General Physics and Astronomy Semiclassical physics 010402 general chemistry 01 natural sciences Molecular physics Spectral line 0104 chemical sciences symbols.namesake Excited state 0103 physical sciences symbols Physical and Theoretical Chemistry Ground state |
| Zdroj: | The Journal of Chemical Physics. 147:224112 |
| ISSN: | 1089-7690 0021-9606 |
| DOI: | 10.1063/1.5003386 |
| Popis: | We report the successful application of a recently developed mixed quantum/semiclassical wave-packet dynamical theory to the calculation of a spectroscopic signal, the linear absorption spectrum of a realistic small-molecule chromophore in a cryogenic environment. This variational fixed vibrational basis/Gaussian bath (FVB/GB) theory avails itself of an assumed time scale separation between a few, mostly intramolecular, high-frequency nuclear motions and a larger number of slower degrees of freedom primarily associated with an extended host medium. The more rapid, large-amplitude system dynamics is treated with conventional basis-set methods, while the slower time-evolution of the weakly coupled bath is subject to a semiclassical, thawed Gaussian trial form that honors the overall vibrational ground state, and hence the initial state prepared by its Franck-Condon transfer to an excited electronic state. We test this general approach by applying it to a small, symmetric iodine-krypton cluster suggestive of molecular iodine embedded in a low-temperature matrix. Because of the relative simplicity of this model complex, we are able to compare the absorption spectrum calculated via FVB/GB dynamics using Heller's time-dependent formula with one obtained from rigorously calculated eigenenergies and Franck-Condon factors. The FVB/GB treatment proves to be accurate at approximately 15-cm-1 resolution, despite the presence of several thousand spectral lines and a sequence of various-order system-bath resonances culminating at the highest absorption frequencies in an inversion of the relative system and bath time scales. |
| Databáze: | OpenAIRE |
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