Session: Physical Chemistry Poster:

Ultrafast two-dimensional infrared (2DIR) spectroscopy is used to learn about rotational and vibrational energy relaxation in dense gases and supercritical fluid solutions, special solvation effects near the critical point, and the evolution of cooperative, liquid phase dynamics as a function of fluid density. 2DIR's capabilities offer a unique tool for identifying co-existing free rotor and liquid-like environments within the same dense fluid sample, evaluating the adequacy of isolated binary collision (IBC) relaxation models in dense gas and near liquid density fluids, and learning about how solute-solvent intermolecular properties separately influence rotational and vibrational relaxation, i.e., energy flow, in those heterogeneous and dynamic environments. Analysis of the 2DIR spectra of the asymmetric stretching band of N₂O in SF₆ and Xe reveals highly efficient rotational energy relaxation rates (1.5-3 collisions), but much slower vibrational energy relaxation rates. A critical slowing effect is found on the rate of rotational relaxation, and liquid-like solvation is observed in dense gas solutions at state points far from the critical region. This 2DIR methodology allows for dynamical and structural details central to chemistry in dense gases and supercritical fluids to be studied with new molecular level detail.

2DIR spectra of the asymmetric stretch rovibrational band of N<sub>2</sub>O solvated in SF<sub>6</sub> at several representative state points ranging from gas to liquid-like exhibit complex lineshapes indicative of a co-existing mixture of free rotors and liquid-like hindered rotors.

2DIR spectra of the asymmetric stretch rovibrational band of N₂O solvated in SF₆ at several representative state points ranging from gas to liquid-like exhibit complex lineshapes indicative of a co-existing mixture of free rotors and liquid-like hindered rotors.

Matthew C Rotondaro

Boston University

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