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Theoretical study of the polarized infrared spectra of the hydrogen bond in 2-furoic acid crystal dimer

机译:2-糠酸晶体二聚体中氢键偏振红外光谱的理论研究

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This work presents a theoretical simulation of νO?H and νO?D band shapes in the polarized infrared spectra of 2-furoic acid dimer crystals measured at liquid-nitrogen temperature. The line shapes are studied theoretically within the framework of the anharmonic couplings between low-frequency hydrogen-bond vibrations and degenerate excited states of high-frequency hydrogen vibrations in hydrogen-bonded dimers and the anharmonic coupling between the first excited state of the fast mode and the harmonics or band combinations of some low-frequency bending modes, which lead to Fermi resonances.This approach takes into account the adiabatic approximation, the intrinsic anharmonicity of the low-frequency mode through a Morse potential, Davydov coupling triggered by resonance exchange between the excited states of the fast modes of the two hydrogen bonds involved in the cyclic dimer, and the direct and indirect damping of the fast-stretching modes of the hydrogen bonds and of the bending modes. The infrared spectral density was calculated within the linear response theory by Fourier transform of the autocorrelation function of the transition dipole moment operator of the fast mode. Numerical results show that mixing of all these effects allows satisfactory reproduction of the main features of the experimental IR line shapes of crystalline H- and D-bonded 2-furoic acid at liquid-nitrogen temperature and for different polarizations.
机译:这项工作提供了在液氮温度下测量的2-糠酸二聚体晶体的偏振红外光谱中νO?H和νO?D能带形状的理论模拟。在氢键二聚体的低频氢键振动与简并的高频氢振动的激发态之间的非谐耦合以及快速模式的第一激发态与第二模式之间的非谐耦合的框架内,对线形进行了理论研究。一些低频弯曲模式的谐波或频带组合会导致费米共振。该方法考虑了绝热近似,通过莫尔斯电势,达维多夫耦合之间的共振交换触发的低频模式的固有非谐性。环状二聚体中两个氢键快速模式的激发态,以及氢键快速拉伸模式和弯曲模式的直接和间接阻尼。在线性响应理论内,通过快速模式的跃迁偶极矩算子的自相关函数的傅立叶变换,计算了红外光谱密度。数值结果表明,所有这些效应的混合可以令人满意地再现液氮温度和不同极化条件下结晶的H-和D键合的2-糠酸的IR线形的主要特征。

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