title: Theoretical and experimental examination of SFG polarization analysis at acetonitrile-water solution surfaces.
abstract: Sum frequency generation (SFG) spectroscopy is widely used to observe molecular orientation at interfaces through a combination of various types of polarization. The present work thoroughly examines the relation between the polarization dependence of SFG signals and the molecular orientation, by comparing SFG measurements and molecular dynamics (MD) simulations of acetonitrile/water solutions. The present SFG experiment and MD simulations yield quite consistent results on the ratios of χ(2)elements, supporting the reliability of both means. However, the subsequent polarization analysis tends to derive more upright tilt angles of acetonitrile than the direct MD calculations. The reasons for discrepancy are examined in terms of three issues; (i) anisotropy of the Raman tensor, (ii) cross-correlation, and (iii) orientational distribution. The analysis revealed that the issues (i) and (iii) are the main causes of errors in the conventional polarization analysis of SFG spectra. In methyl CH stretching, the anisotropy of Raman tensor cannot be estimated from the simple bond polarizability model. The neglect of the orientational distribution is shown to systematically underestimate the tilt angle of acetonitrile. Further refined use of polarization analysis in collaboration with MD simulations should be proposed.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. morita@tohoku.ac.jp.
authors.forename: Kengo
authors.initials: K
authors.lastname: Saito
authors.affiliation: Institute for Catalysis, Hokkaido University, Kita-ku, Sapporo 001-0021, Japan. ye@cat.hokudai.ac.jp.
authors.forename: Qiling
authors.initials: Q
authors.lastname: Peng
authors.affiliation: Institute for Catalysis, Hokkaido University, Kita-ku, Sapporo 001-0021, Japan. ye@cat.hokudai.ac.jp.
authors.forename: Lin
authors.initials: L
authors.lastname: Qiao
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. morita@tohoku.ac.jp and Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto 615-8520, Japan.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. morita@tohoku.ac.jp.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Joutsuka
authors.affiliation: Department of Applied Chemistry, Graduate School of Science and Engineering, University of Toyama, Toyama 930-8555, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ishiyama
authors.affiliation: Institute for Catalysis, Hokkaido University, Kita-ku, Sapporo 001-0021, Japan. ye@cat.hokudai.ac.jp and Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto 615-8520, Japan.
authors.forename: Shen
authors.initials: S
authors.lastname: Ye
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. morita@tohoku.ac.jp and Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto 615-8520, Japan.
authors.forename: Akihiro
authors.identifier: http://orcid.org/0000-0002-2104-0605
authors.initials: A
authors.lastname: Morita