| Research Abstract |
To understand the mechanism of electron transfer dynamics at solid/liquid interfaces, information of structures of molecules at electrode/electrolyte interface including short-lived intermediates and solvent at the interface is essential. The determination of the interfacial structures of the intermediate and solvent is, however, difficult by conventional surface vibrational techniques because of small number of molecules compared to bulk molecules. Temporal vibration of vibrational modes induced by electronic excitation is monitored by IR adsorption and surface-specific sum frequecy generation (SFG) techniques. We investigated the relations between interfacial structures and reaction dynamics by using these spectroscopic methods.
1. Observation and dynamics of adsorbates at solid/liquid interfaces by SFG spectroscopy
Dynamics of adsorbed CO on Pt electrode was followed by visible pump SFG probe measurements. An SFG peak due to adsorbed CO at on-top site of Pt was observed at 2064cm-l. T
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he intensity of this peak decreased quickly upon excitation and recovered within few ten of os. A new broad peak was observed at 1980cm-l corresponding to adsorbed CO at multi-fold site, suggesting the site exchange upon excitation. The recovery rate was found to be dependent on potential.
2. Carrier and charge transfer dynamics by visible pump-visible and IR technique
Time-resolved visible-pump visible and infrared-probe techniques, in which very short UV or visible pulse excitation is combined with delayed ultrafast visible and mid-IR absorption, respectively, are powerful tools to monitor the changes in electronic and molecular structure, respectively, as after the photoexcitation. In the present study, (1) a system, which allows these two measurements, was constructed, (2) visible-pump infrared-probe technique was applied to study the effect of size and surface treatment on the carrier dynamics of CdS, and (3) visible-pump visible and infrared-probe techniques were applied to study the photo-induced intra-molecular charge transfer with a triruthenium complex [Ru_3(O)(CH_3CO2)_6(CO)L_2], where L=ligands, containing a strongly IR active ligand, CO, which act as a direct IR probe of the electron density at the metal center.
3. Characterization of water structure at biomaterial surfaces
Many biological systems such as proteins and enzymes are inactive without water. For a complete understanding of the function of such systems, information of the structure and dynamics of the water is essential. We incestigated the structure of water at several biomaterial surfaces. For example, we monitored the structure of interfacial water at hydro-polymer gel/solid interface by SFG spectroscopy under various pressures. The contribution of weakly hydorogen bonded water in SFG spectra increased with pressure, suggesting the inportant role of weakly hydorogen bonded water to the low friction properties at the hydro-polymer gel/solid interfaces. Less
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