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Quantum State-Resolved Energy Transfer Dynamics at the Gas–Liquid Interface

TitleQuantum State-Resolved Energy Transfer Dynamics at the Gas–Liquid Interface
Publication TypeThesis
Year of Publication2009
AuthorsPerkins, BG

The objective of this thesis involves understanding the dynamics of the interaction between a gas and liquid molecules at the interface. High resolution infrared spectroscopy is used to detect the energy transfer between CO2 and various liquids, where the dynamics are determined from the final distributions for translation, rotation, and vibration of the scattered projectile. Supersonic molecular beams are employed to control the incident energy, angle, and internal state populations. Refreshed liquid surfaces are prepared to ensure the incident CO2 strikes the intended target in an effort to understand the nascent interactions. In general, direct absorption of infrared laser light (λ = 4.2 μm) is used to determine the quantum state populations in the scattered CO2 flux.

The energy transfer dynamics depend on the initial conditions of the system. Studies have investigated the ways in which incident energy, angle, and surface temperature effect the interactions at the interface. In each case, nonequlibrium dynamics are explored through a simple two-channel model that characterizes the final distribution in terms of trapping-desorption (TD) and impulsive scattering (IS) populations. Experimental efforts have focused on measurements that elucidate the characteristics of both channels, where high resolution Doppler broadened absorption profiles have been recorded for a series of final angles that span the entire 2π steradian hemispherical scattering volume.

In parallel with experimental studies, theoretical molecular dynamics (MD) simulations have provided a detailed description of the interaction from a microscopic point of view. In these studies, CO2 is scattered from a perfluorinated self assembled monolayer (F-SAM), which has been used to model the liquid. Ensembles of trajectories have been calculated for conditions that match those from experiment. Final distributions have been analyzed within the two-channel scattering model, where the results quantitatively agree with the experimental studies of incident energy, angle, and surface temperature. On the basis of this comparison, further details of the scattering dynamics are extracted to characterize the three-dimensional flux, velocity, and angular momentum distributions. In addition, the simulations provide residence time distributions that parallel the two-temperature model, but for which the dynamics are characterized by the number of interactions.