RESUMEN
We attempted to theoretically characterize internal vibrational relaxation and energy relaxation pathways due to anharmonicity in polyatomic molecules. Energy transport dynamics have been modeled based on a generalization of Marcus electron transfer theory. Modifications have been made to our previously developed theory in order to improve the description of internal vibrational dynamics. We applied our method to several molecules studied experimentally by relaxation-assisted two-dimensional infrared spectroscopy (RA 2DIR). The theoretical predictions were found to be consistent with the majority of the experimental data.
RESUMEN
Vibrational energy relaxation and transport in a molecule that is far from thermal equilibrium can affect its chemical reactivity. Understanding the energy transport dynamics in such molecules is also important for measuring molecular structural constraints via relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy. In this paper we investigated vibrational relaxation and energy transport in the ortho, meta, and para isomers of acetylbenzonitrile (AcPhCN) originated from excitation of the CN stretching mode. The amplitude of the cross-peak among the CN and CO stretching modes served as an indicator for the energy transport from the CN group toward the CO group. A surprisingly large difference is observed in both the lifetimes of the CN mode and in the energy transport rates for the three isomers. The anharmonic DFT calculations and energy transport modeling performed to understand the origin of the differences and to identify the main cross-peak contributors in these isomers described well the majority of the experimental results including mode excited-state lifetimes and the energy transport dynamics. The strong dependence of the energy transport on molecular structure found in this work could be useful for recognizing different isomers of various compounds via RA 2DIR spectroscopy.