Development of time-resolved and two-dimensional infrared spectroscopy for dynamic studies of solid/liquid interfaces

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We have developed a novel infrared spectroscopy technique that enables real-time monitoring of reactions and dynamics at solid/liquid interfaces. This technique uses three advanced infrared technologies, surface-enhanced infrared absorption spectroscopy (SEIRAS), time-resolved FT-IR,and two-dimensional correlation analysis (2D-IR).SEIRAS probes the interface without the interference from the bulk solution at a very high sensitivity. Owing to the high sensitivity of SEIRAS,high-speed spectral measurements with rapid-scan and step-scan FT-IR inferferometry becomes possible. We have succeeded for the first time to monitor electrochemical reactions with time-resolutions ranging from microseconds to milliseconds. By the success of the time-resolved spectra measurements, the molecular information obtained from the spectra became to be directly correlated with the kinetic information obtained from conventional electrochemical measurements.The time-resolved spectra collected during reactions a … More re often complex due to the overlapping of absorption bands of reactants and products. To differentiate spectral features of the species by using their characteristic time-dependent behaviors, 2D correlation analysis technique was employed. The basic concept of 2D-IR is somewhat analogous to that of 2D correlation technique used in NMR.It was found that 2D-IR accentuates certain dynamic information that is not readily seen in the one-dimensional time-resolved spectra. One of the important characters of 2D-IR is that the time-sequence of the intensity changes of the bands arising from different species can be determined. This character is very useful in the studies of reaction processes.We have demonstrated the utilities of the developed technique through studies of several electrochemical reactions. One of the most significant achievements in this project is the success in the analysis of the "double-layr" structure. We found that water molecules reorient at the Au (111) electrode surface depending upon the surface charge. The results are in good agreement with recent molecular dynamics simulations of the double-layr. Less