Mixed Quantum/Semiclassical studies of spectroscopy and dynamics

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

In this project funded by the Chemical Theory, Models and Computational Methods program of the Chemistry Division, Professor Jeffrey A. Cina of the University of Oregon is developing theoretical methods for simulating and interpreting time-dependent laser-based measurements of low-temperature materials that absorb light. The molecular-based approach, that approximates the quantum mechanical behavior, makes it possible to carry out efficient calculations despite the complexity of these systems. This method also allows the interpretation of these processes in terms of motion, easily visualized, of the participating molecules and atoms. The theoretical framework under development is termed a fixed vibrational basis/Gaussian bath description. For the purpose of simulating spectroscopy signals, it is being developed in perturbative form with respect to the electric field strengths of several external laser pulses. The theory describes the microscopic dynamics of many-body chemical systems in terms of a physically motivated set of time-dependent parameters that are small in number compared with the collection of linear coefficients that are required in a direct basis-set expansion. Initial applications are being made to resonantly driven small-molecule targets embedded in rare-gas host crystals. Systems of this kind display many generic features of condensed-phase chemical dynamics, while being both challenging, due to the prominence of quantum mechanical effects at cryogenic temperatures, and amenable to a mixed quantum/semi-classical treatment. The quality of the calculated signals is being assessed by comparison with extensive experimental data and more computationally intensive theoretical results, including multi-configuration time-dependent Hartree calculations.