Terahertz (THz) absorption is a fingerprint property of materials, due to the underlying low-frequency vibration/phonon modes being strongly dependent on the chemical constitutions and microscopic structures. The low excitation energies (0.414−41.4 meV) are related to two intrinsic properties of THz vibrations: the potential energy surfaces (PESs) are shallow, and the vibrationally excited states are usually populated via thermal fluctuations. The shallow PESs make the vibrations usually anharmonic, leading to redshifted vibrational excited state absorption; combined with considerable vibrational excited states population, characteristic THz signals are usually redshifted and congested with varying degrees at different temperatures. Combining existing experimental THz spectra at low temperatures, first principles vibration analysis, and the Morse potential, we developed a semi-empirical model to evaluate the anharmonicity of the low-frequency modes. The model was benchmarked with purine molecular crystal to generate THz spectra at different temperatures, the results were consistent with experiments. The good agreement suggests this model would facilitate the application of THz spectroscopy in molecular crystal characterization.
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February 2023
Research Article|
February 01 2023
Semi-Empirical model to retrieve finite temperature terahertz absorption spectra using Morse potential
Special Collection:
Virtual Issue on Molecular Spectroscopy (2023)
Huifang Ma;
Huifang Ma
a
School of Materials Science and Engineering, China University of Petroleum (East China)
, Qingdao 266580, China
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Yanzhao Yang;
Yanzhao Yang
b
The 41st Institute of China Electronics Technology Group Corporation
, Qingdao 266555, China
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Heng Jing;
Heng Jing
b
The 41st Institute of China Electronics Technology Group Corporation
, Qingdao 266555, China
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Wanshun Jiang;
Wanshun Jiang
b
The 41st Institute of China Electronics Technology Group Corporation
, Qingdao 266555, China
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Wenyue Guo;
Wenyue Guo
*
a
School of Materials Science and Engineering, China University of Petroleum (East China)
, Qingdao 266580, China
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Chin. J. Chem. Phys. 36, 15–24 (2023)
Article history
Received:
February 19 2022
Accepted:
February 28 2022
Citation
Huifang Ma, Yanzhao Yang, Heng Jing, Wanshun Jiang, Wenyue Guo, Hao Ren; Semi-Empirical model to retrieve finite temperature terahertz absorption spectra using Morse potential. Chin. J. Chem. Phys. 1 February 2023; 36 (1): 15–24. https://doi.org/10.1063/1674-0068/cjcp2202032
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