Study on Infrared Absorption Spectra of Ethanol in Small Slits
LIU Yun, LI Chun, GUO Da-bo, LEI Wen*, YUAN Guang*
College of Physics and Optoelectronic Engineering, Ocean University of China, Engineering Research Center of Ministry of Education for High-end Instruments and Equipment of Marine Physics, Qingdao 266100, China
Abstract：Infrared (IR) spectroscopy is a tool routinely used to analyze substances. It is based on the resonant absorption of infrared radiation by molecular vibrations to obtain information about the structure and chemical composition of a sample. IR enhancement is a crucial topic in IR research, and increasing the IR absorption range is a common approach. However, IR enhancement under small cavity conditions has unique application requirements. The enhancement of infrared radiation capacity within the small cavity suggests the potential for increased infrared absorption. In this study, the infrared spectral absorption properties of ethanol molecules in slit cavities are investigated. A wedge-shaped slit structure was developed, creating slit regions of varying thicknesses between the double-polished single-crystal silicon wafer and zinc selenide plate, with slit thicknesses less than 1 μm, along with an external temperature control device. The temperature dependence of the infrared absorption of ethanol in slits of different thicknesses was investigated. The infrared absorption spectrum of ethanol exhibits prominent absorption peaks in the wavenumber ranges of 3 690~2 650 and 1 150~1 010 cm-1. The variations in the positions of the main absorption peaks and the non-absorption peaks of ethanol with temperature were compared. It was found that the absorbance at the non-absorption peaks increases with the intensity of blackbody radiation. In contrast, the intensity at the main absorption peaks of ethanol decreases relative to the intensity of blackbody radiation. This reflects that the radiative capacity of ethanol molecules in the slit decreases with temperature. For different Slit thicknesses, the absorbance of ethanol molecules at the same temperature varies. The maximum absorbance for different vibrational modes corresponds to different slit thicknesses. The slit thickness that shows the maximum absorbance at wavenumbers of 3 335, 2 975, 2 930, and 2 881 cm-1 is 0.73 μm. For the wavenumbers of 1 090 and 1 050 cm-1, the slit thickness that exhibits the best enhancement in absorbance is greater than or equal to 0.64 μm. These results show that the slit cavity can enhance the IR absorption of ethanol molecules; however, different vibrational modes of ethanol molecules correspond to different optimal slit thicknesses. The absorption coefficients of the characteristic absorption peaks of ethanol decrease with increasing temperature.
刘 赟，李 春，郭大勃，雷 文，元 光. 微小狭缝中乙醇的红外吸收光谱研究[J]. 光谱学与光谱分析, 2025, 45(09): 2543-2549.
LIU Yun, LI Chun, GUO Da-bo, LEI Wen, YUAN Guang. Study on Infrared Absorption Spectra of Ethanol in Small Slits. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2025, 45(09): 2543-2549.
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