Novel Surface Phenomena
Abstract
The major goal in this project is to study dangling OH bonds at a water interface by comparing theory and experiment for SFG, a surface sensitive spectroscopy method. In this work we developed a method to calculate absolute intensities in SFG, to make a more quantitative comparison with the experimental data, rather than calculating only the conventional relative SFG intensities in the spectrum. It will be recalled that SFG involves both an infrared laser and a visible laser as input and the combined outgoing signal as output and that as a consequence of this "nonlinearity" (response to the product of two signals) this response has zero signal in a centrosymmetric system, such as the interior of a liquid. It is thereby a highly sensitive technique for studying the composition of interfaces, in the present case a water-air interface. In SFG experiments the infrared and a visible laser are used to illuminate an interface at a glancing angle and the intensity of the combined outgoing beam is measured. Different polarization combinations of the three beams are studied. We studied the dangling OH groups at a water surface, groups that are believed to be involved in catalysis of organic reactions at surfaces in water organic emulsions. The dangling OH gives rise to a narrow peak in the spectrum around 3750 cm(-1). The immediate goal was to see if, using polarizability and infrared and Raman spectroscopic data on OH groups in H20vapor (where there are no hydrogen bonds)) we could use molecular dynamics trajectories to predict the absolute values of the frequency-dependent SFG susceptibility for the dangling OH groups. Previously, relative intensities had been extensively studied theoretically and compared with experiment.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 26, 2022
- Accession Number
- AD1192472
Entities
People
- Rudolph A. Marcus
Organizations
- California Institute of Technology