We measured the terahertz spectra of five powdered vitamins, nicotinamide, nicotinic acid, ascorbic acid, pyridoxine hydrochloride, and biotin, to investigate intermolecular hydrogen bonding. These vitamins have various weak to moderate hydrogen bonds between molecules and thus are good candidates for the investigation of various hydrogen bond stretching. Using dispersion-corrected density functional theory calculations on a periodic system, we assigned the observed THz peaks with excellent accuracy. The stretching vibrations of the intermolecular hydrogen bonds are mixed with the intermolecular translational and rotational modes. Depending on the strength of the hydrogen bond and the mass of the moiety linked via the hydrogen bond, the wavenumber of each type of hydrogen bond is located within a limited region. According to the present study, the stretching vibration of a weak hydrogen bond located at approximately 60–105 cm⁻¹ is summarized as having a sharp full width at half maximum of 1–2 cm⁻¹ and the molar extinction coefficient of 4–10 M⁻¹ cm⁻¹. The anharmonicity of the potential energy curve was found in modes containing weak intermolecular NH⋯N and NH⋯O stretching vibrations. Present research on the specific properties of hydrogen bond stretching vibrations observed in the THz region provides useful information for quickly estimating the existence of intermolecular hydrogen bonds.

中文翻译：

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在结晶维生素的太赫兹光谱中观察到的分子间氢键拉伸振动†

我们测量了五种粉状维生素，烟酰胺，烟酸，抗坏血酸，盐酸吡ido醇和生物素的太赫兹光谱，以研究分子间的氢键作用。这些维生素在分子之间具有各种弱至中度的氢键，因此是研究各种氢键伸展的良好候选者。在周期系统上使用色散校正的密度泛函理论计算，我们以极好的精度分配了观察到的太赫兹峰。分子间氢键的拉伸振动与分子间平移和旋转模式混合。取决于氢键的强度和通过对于氢键，每种类型的氢键的波数位于有限的区域内。根据目前的研究，一个弱的氢键在大约60–105 cm ^-1处的拉伸振动被总结为在一半的最大值处具有锐利的全宽度1-2 cm ^-1，摩尔消光系数为4–10。 M ^-1 cm ^-1。在包含弱分子间NH⋯N和NH⋯O拉伸振动的模式中发现了势能曲线的非谐性。目前对在太赫兹区域中观察到的氢键拉伸振动的特定性质的研究为快速估计分子间氢键的存在提供了有用的信息。