Laman N, Harsha S Sree, Grischkowsky D
School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
Appl Spectrosc. 2008 Mar;62(3):319-26. doi: 10.1366/000370208783759768.
Low frequency vibrational modes of pharmaceutical molecules are dependent on the molecule as a whole and can be used for identification purposes. However, conventional Fourier transform far-infrared spectroscopy (FT-IR) and terahertz time-domain spectroscopy (THz-TDS) often result in broad, overlapping features that are difficult to distinguish. The technique of waveguide THz-TDS has been recently developed, resulting in sharper spectral features. Waveguide THz-TDS consists of forming an ordered polycrystalline film on a metal plate and incorporating that plate in a parallel-plate waveguide, where the film is probed by THz radiation. The planar order of the film on the metal surface strongly reduces the inhomogeneous broadening, while cooling the waveguide to 77 K reduces the homogeneous broadening. This combination results in sharper absorption lines associated with the vibrational modes of the molecule. Here, this technique has been demonstrated with aspirin and its precursors, benzoic acid and salicylic acid, as well as the salicylic acid isomers 3- and 4-hydroxybenzoic acid. Linewidths as narrow as 20 GHz have been observed, rivaling single crystal measurements.
药物分子的低频振动模式取决于整个分子，可用于识别目的。然而，传统的傅里叶变换远红外光谱（FT-IR）和太赫兹时域光谱（THz-TDS）常常产生宽泛、重叠的特征，难以区分。波导太赫兹时域光谱技术最近得到了发展，产生了更尖锐的光谱特征。波导太赫兹时域光谱包括在金属板上形成有序的多晶薄膜，并将该金属板纳入平行板波导中，在其中用太赫兹辐射探测薄膜。金属表面薄膜的平面有序性极大地减少了非均匀展宽，而将波导冷却到77 K则减少了均匀展宽。这种结合导致了与分子振动模式相关的更尖锐的吸收线。在此，该技术已通过阿司匹林及其前体苯甲酸和水杨酸以及水杨酸异构体3-羟基苯甲酸和4-羟基苯甲酸得到了验证。已观察到窄至20 GHz的线宽，可与单晶测量相媲美。
