標題: Anharmonic coupling of the CH-stretch and CH-bend vibrations of chloroform as studied by near-infrared electroabsorption spectroscopy
作者: Nishida, Jun
Shigeto, Shinsuke
Yabumoto, Sohshi
Hamaguchi, Hiro-o
應用化學系
應用化學系分子科學碩博班
Department of Applied Chemistry
Institute of Molecular science
關鍵字: density functional theory;infrared spectra;organic compounds;transition moments;vibrational modes
公開日期: 21-十二月-2012
摘要: Combination bands that involve CH- or OH-stretch vibrations appear in the near-infrared (NIR) region (4000-10 000 cm(-1)). Because they arise from anharmonic coupling between the component fundamentals, detailed analysis of the frequency and intensity of NIR combination bands allows one to elucidate the mechanisms behind the vibrational coupling in the condensed phase in terms of mechanical and electrical anharmonicities. Nevertheless, little has been studied, in particular experimentally, on the origin of the combination band intensity. Here, we show that NIR electroabsorption (EA) spectroscopy, which directly probes the effects of an externally applied electric field on a combination band, can shed new light on anharmonic vibrational coupling through determination of the direction of the transition moment for the combination band. We studied the combination band of the CH-stretch (nu(1)) and CH-bend (nu(4)) modes of liquid chloroform. The electric-field induced absorbance change of the nu(1) + nu(4) combination band caused by reorientation of the chloroform molecule was measured at various chi angles, where chi is the angle between the direction of the applied electric field and the polarization of the incident IR light. We were able to detect an absorbance change as small as 5 x 10(-8) for the combination band. Using the NIR EA spectra of the combination band together with those of the CH-stretch and bend fundamentals, the angle between the transition moment for the combination band and the permanent dipole moment was determined experimentally for the first time to be (79 +/- 14)degrees. The present investigation indicates that the contribution of the CH-stretch mode to the mechanical anharmonicity is minor and that the CH-bend mode plays a dominant role in the mechanical part of the vibrational coupling between the two fundamentals. Furthermore, density functional theory calculations show that both the mechanical anharmonicity of the CH-bend mode and the electrical anharmonicity may contribute equally to the anharmonic coupling. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770264]
URI: http://dx.doi.org/10.1063/1.4770264
http://hdl.handle.net/11536/21298
ISSN: 0021-9606
DOI: 10.1063/1.4770264
期刊: JOURNAL OF CHEMICAL PHYSICS
Volume: 137
Issue: 23
結束頁: 
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  1. 000312780300028.pdf