서강대학교

초록/요약

Sum-frequency spectra from Langmuir monolayer of pentadecanoic acid at different temperatures were investigated by two-dimensional correlation analysis. Alkyl chains in the fatty acid monolayer are expected to have more gauche conformation rather than all-trans conformation at higher temperatures, which was readily probed by the change in the sum-frequency spectra. The two-dimensional correlation analysis was applied to show subtle spectral features which are hardly visible in the conventional sum-frequency analysis. Relative changes of the spectral components with temperature stood out, and closely spaced peaks which are hard to distinguish in the raw spectrum were clearly resolved in the two-dimensional correlation maps. Some peaks in the correlation maps, however, were found out to be shifted from the original positions in the spectrum, which is considered to come from interference due to the coherent nature of the sum-frequency spectroscopy. Phase-sensitive sum-frequency experiment to acquire the field amplitude of sum-frequency response and the two-dimensional analysis of the amplitude spectra at different temperatures reduced those artifacts.