COLL 94 |
| Brian Space, Chemistry, University of South Florida, 4202 E. Fowlwer Ave. SCA400, Dept. Chem.T, Tampa, FL 33620-5250 and Angela Perry, Department of Chemistry SCA400, University of South Florida, Tanpa, FL 33620. |
| Theoretical approximations to the interface specific sum frequency generation (SFG) spectrum of O-H stretching at the water/vapor interface are constructed using time correlation function (TCF) and instantaneous normal mode (INM) methods. Both approaches lead to a (SSP polarization geometry) signal in excellent agreement with experimental measurements; the SFG spectrum of the entire water spectrum, both intermolecular and intramolecular, is reported. The observation that the INM spectrum is in agreement with the TCF result implies that motional narrowing effects play no role in the interfacial lineshapes, in contrast to the O-H stretching dynamics in the bulk that leads to a narrowed lineshape. This implies that (SSP) SFG spectroscopy is a probe of structure with dynamics not represented in the signal. The INM approach permits the elucidation of the molecular basis for the observed signal, and the motions responsible for the SFG lineshape are well approximated as local O-H stretching modes. The complexity of the broad structured SFG signal is due to O-H stretching motions facing toward the bulk or vacuum environments that are characteristic of the interface. The success of both approaches suggests that theory can play a crucial role in interpreting SFG spectroscopy at more complex interfaces. |
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Vibrational Analyses of Dry and Wet Surfaces
8:30 AM-11:30 AM, Monday, March 29, 2004 Marriott -- Grand Ballroom H, Oral
Division of Colloid and Surface Chemistry |