Zhongwei Zhang, Zhi Zhu, Minghui Yuan, Minghui Li, Guanjun You, Lin Chen, Yiming Zhu
https://www.sciencedirect.com/science/article/abs/pii/S0030401819309782
Directly predicting the line positions of samples in the terahertz (THz) band is of significant importance for their THz identification. However, it is really a challenge to gain accurately the line positions by means of theoretical calculation, because the calculation typically involves various parameters, such as level energy and transition moment, which usually we hardly get directly. Based on the classical forced vibration model of dipoles, we propose a quantitative expression, i.e. the forced radiation intensity of molecular electric dipoles, which intend to predict the line positions of absorption peaks in the THz fingerprint spectra of a sample. We verified our expression by 9 recognized frequencies selected from the fingerprint spectra of water vapor in the THz band. Both the line positions and intensities of the absorption peaks of water vapor we calculated by the expression are well consistent with the experimental measurements. The line positions we calculated are also more accurate and comprehensive than that of water clusters simulated from Density Functional Theory (DFT). Our findings further support the theory of coherent superposition to advance a new method to exactly analyze the generation mechanism of molecular THz-fingerprint spectroscopy of a sample.
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