Solute vibrational relaxation at liquid interfaces

The rate and mechanism of vibrational energy and phase relaxation in condensed media are both determined by the structure and the nature of the solute-solvent interactions. Vibrational relaxation is of fundamental importance for understanding chemical reaction dynamics. Although many experimental and theoretical studies have focused on the relaxation of solute molecules in bulk liquids, ° far less has been done at liquid surfaces. 

No direct measurements of the vibrational lifetime of solute molecules at liquid/vapor and liquid/liquid interfaces have been reported to date. However, vibrational energy relaxation times of N3, NCO , and NCS inside the water pools of reverse micelles were measured and found to be about three times longer than in bulk water.There are also several studies using time-resolved SFG measurements at liquid interfaces, which can follow vibrational spectral evolution, examining neat water at liquid/vapor and liquid/solid interfaces. 

Given our current knowledge about the neat liquid interface structure and dynamics, the basic question regarding vibrational relaxation at liquid interfaces is how do these structures and dynamics affect the relaxation rate Are the same factors responsible for relaxation in bulk liquids applicable to relaxation at liquid interfaces, or, are there unique surface effects that also need to be taken into account  

To focus on the question of surface effects on vibrational energy relaxation rate, without the complications of intramolecular energy flow, Benjamin and coworkers studied the vibrational relaxation of a diatomic solute molecule (single vibrational mode) at various liquid/vapor and liquid/liquid interfaces. The solute is modeled using the Morse potential  

The computational approach employs nonequilibrium classical trajectories to determine the rate. The solute is prepared with an initial vibrational 

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