02057nas a2200217   4500008004100000245008000041210006900121260011700190300003200307490000900339520122200348100001701570700002201587700002501609700002001634700002001654700002201674700001801696700001701714856010801731       2014                        eng d00aDesign and engineering of organic molecules for customizable terahertz tags0 aDesign and engineering of organic molecules for customizable ter  aSan Francisco, CAbSPIE-Int Soc Optical Engineering, 1000 20th ST, PO Box 10, Bellingham, WA 98227-0010 USAcFEB  aArticle Number: UNSP 89850P0 v89853 a<p>Terahertz (THz) frequency band lies between the microwave and infrared region of the electromagnetic spectrum. Molecules having strong resonances in this frequency range are ideal for realizing "Terahertz tags" which can be easily incorporated into various materials. THz spectroscopy of molecules, especially at frequencies below 10 THz, provides valuable information on the low frequency vibrational modes, viz. intermolecular vibrational modes, hydrogen bond stretching, torsional vibrations in several chemical and biological compounds. So far there have been very few attempts to engineer molecules which can demonstrate customizable resonances in the THz frequency region. In this paper, Diamidopyridine (DAP) based molecules are used as a model system to demonstrate engineering of THz resonances (&lt; 10 THz) by fine-tuning the molecular mass and bond strengths. Density Functional Theory (DFT) simulations have been carried out to explain the origin of THz resonances and factors contributing to the shift in resonances due to the addition of various functional groups. The design approach presented here can be easily extended to engineer various organic molecules suitable for THz tags application.</p>1 aRay, Shaumik1 aDash, Jyotirmayee1 aNallappan, Kathirvel1 aKaware, Vaibhav1 aBasutkar, Nitin1 aAmbade, Ashootosh1 aJoshi, Kavita1 aPesala, Bala  uhttps://library.ncl.res.in/content/design-and-engineering-organic-molecules-customizable-terahertz-tags02651nas 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