02651nas a2200241   4500008004100000022001400041245011100055210006900166260007100235300001400306490000800320520176800328100002202096700001802118700002502136700002002161700002402181700002402205700002602229700001802255700001702273856011902290       2015                        eng d  a1089-563900aTerahertz spectroscopy and solid-state density functional theory calculations of cyanobenzaldehyde isomers0 aTerahertz spectroscopy and solidstate density functional theory   a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcJUL  a7991-79990 v1193 a<p>Spectral signatures in the terahertz (THz) frequency region are mainly due to bulk vibrations of the molecules. These resonances are highly sensitive to the relative position of atoms in a molecule as well as the crystal packing arrangement. To understand the variation of THz resonances, THz spectra (2-10 THz) of three structural isomers: 2-, 3-, and 4-cyanobenzaldehyde have been studied. THz spectra obtained from Fourier transform infrared (FTIR) spectrometry of these isomers show that the resonances are distinctly different especially below 5 THz. For understanding the intermolecular interactions due to hydrogen bonds, four molecule cluster simulations of each of the isomers have been carried out using the B3LYP density functional with the 6-31G(d,p) basis set in Gaussian09 software and the compliance constants are obtained. However, to understand the exact reason behind the observed resonances, simulation of each isomer considering the full crystal structure is essential. The crystal structure of each isomer has been determined using X-ray diffraction (XRD) analysis for carrying out crystal structure simulations. Density functional theory (DFT) simulations using CRYSTAL14 software, utilizing the hybrid density functional B3LYP, have been carried out to understand the vibrational modes. The bond lengths and bond angles from the optimized structures are compared with the XRD results in terms of root-mean-square-deviation (RMSD) values. Very low RMSD values confirm the overall accuracy of the results. The simulations are able to predict most of the spectral features exhibited by the isomers. The results show that low frequency modes (&lt;3 THz) are mediated through hydrogen bonds and are dominated by intermolecular vibrations.</p>1 aDash, Jyotirmayee1 aRay, Shaurnik1 aNallappan, Kathirvel1 aKaware, Vaibhav1 aBasutkar, Nitin, B.1 aGonnade, Rajesh, G.1 aAmbade, Ashootosh, V.1 aJoshi, Kavita1 aPesala, Bala  uhttps://library.ncl.res.in/content/terahertz-spectroscopy-and-solid-state-density-functional-theory-calculations-0