Suzuki Yudai, Nojima Yuki, Yamaguchi Shoichi
Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University , 255 Shimo-Okubo, Sakura, Saitama 338-8570, Japan.
J Phys Chem Lett. 2017 Apr 6;8(7):1396-1401. doi: 10.1021/acs.jpclett.7b00312. Epub 2017 Mar 15.
Unraveling vibrational coupling is the key to consistently interpret vibrational spectra of complex molecular systems. The vibrational spectrum of the water surface heavily suffers from vibrational coupling, which hinders complete understanding of the molecular structure and dynamics of the water surface. Here we apply heterodyne-detected sum frequency generation spectroscopy to the water surface and accomplish the assignment of a weak vibrational band located at the lower energy side of the free OH stretch. We find that this band is due to a combination mode of the hydrogen-bonded OH stretch and a low-frequency intermolecular vibration, and this combination band appears in the surface vibrational spectrum through anharmonic vibrational coupling that takes place exclusively at the topmost surface.
解开振动耦合是连贯解释复杂分子体系振动光谱的关键。水面的振动光谱深受振动耦合之苦，这阻碍了对水面分子结构和动力学的全面理解。在此，我们将外差检测和频产生光谱应用于水面，并完成了对位于自由OH伸缩振动较低能量侧的一个弱振动带的归属。我们发现，该谱带归因于氢键OH伸缩振动与低频分子间振动的一种组合模式，并且这种组合带通过仅在最顶层表面发生的非谐振动耦合出现在表面振动光谱中。
