Abstract
The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz) spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating noncovalent interactions has established the position of THz spectroscopy as a powerful tool for detecting the weak bonding in crystals. In this review, we are going to introduce, briefly, the contribution of weak bonds in the construction of molecular crystals first, and then, we will review THz spectroscopy as a powerful tool for detecting the formation of weak bonds and will show the significant contribution of advanced computational codes in treating noncovalent interactions. From the second section, following the Introduction, to the seventh section, before the conclusions, we describe: (1) the crystal packing forces, the hydrogen-bonded networks and their contribution to the construction of organic crystals; (2) the THz vibrations observed in hydrogen-bonded molecules; (3) the computational methods for analyzing the THz vibrations of hydrogen-bonded molecules; (4) the dispersion correction and anharmonicity incorporated into the first-principles calculations and their effect on the peak assignment of the THz spectrum (5) the temperature dependence; and (6) the polarization dependence of the THz spectrum.
Highlights
Terahertz (THz) vibrations in the frequency range of 30–200 cm−1 give direct evidence for the formation of weak bonds in crystals
The method enables the identification of explosives, chemical and biological agents through their characteristic fingerprint in the THz spectrum That weak intermolecular interactions in crystals provide a spectroscopic profile with strongly individual characteristics in the THz region, i.e., the THz method is very sensitive to the weak intermolecular interactions in crystals, enables the unambiguous identification of materials
This review is intended to give a coherent survey of the weak bond in assembling molecular crystals, of THz spectroscopy as a powerful tool for detecting the formation of weak bonds in crystals and of the significant contribution of advanced computational codes to analyze the THz spectrum
Summary
Terahertz (THz) vibrations in the frequency range of 30–200 cm−1 give direct evidence for the formation of weak bonds in crystals. The contributions and efforts in the field of materials research and crystal engineering [1,2,3,4,5,6,7], those joined with the hydrogen bonding interactions in the field of THz spectroscopy, have resulted in a wide range of implementations of this method in practice in spectroscopic imaging [8], environmental inspection and detection [9], public security [10,11], biomedical analysis [12,13] and wireless communications [14,15,16,17]. Along with materials research and crystal engineering, i.e., the species interactions in crystals are focused mainly on inorganic materials, organic materials research found a place in THz generation and detection Such materials have shown great potential and broadband THz properties (10–1000 cm−1), extending the possibility of THz spectroscopy for the identification of materials in the mid-IR (infrared) region.
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