Analytical Sciences

Electron-Enhanced Vibrational Spectroscopy: A Theoretical Approach

Hiroharu YUI,*^,** Takahito NAKAJIMA,*** Kimihiko HIRAO,*** and Tsuguo SAWADA**

*Department of Chemistry, Faculty of Science, Tokyo University of Science, 12 Funagawaramachi, Ichigaya, Shinjuku, Tokyo 162-0826, Japan
**PRESTO-JST, Sanbancho 5, Chiyoda, Tokyo 102-0075, Japan
***Department of Applied Chemistry, Faculty of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan

Enhancement of the Raman scattering and IR absorption activities due to the electron-attachment was investigated for water systems by DFT calculations. DFT calculation of a 6-ring water cluster system that included the diffusive nature of electrons well reproduced the Raman enhancement effects and Raman shifts of the OH stretching modes observed in experiments. Based on the same model and calculations, enhancement of the IR absorption activity was also studied and was found to also be improved. Furthermore, the same calculation revealed that the enhancement can be also expected not only in the OH stretching but also in the lower wavenumber region. The enhancement factors for the various vibrational modes of the OH groups range from 10² - 10⁵ thanks to the electron addition. Based on the coincidence between the theoretical model and the experimental results for the Raman signals and theoretical prediction for IR absorption, new enhancement techniques based on an electron-attachment in both Raman scattering and IR absorption, denoted as “electron-enhanced vibrational spectroscopy (EEVS)”, is proposed, where molecular polarizability itself is modulated by the strong electrostatic field induced by neighboring electrons.

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