Vibrational Spectroscopic Analysis of Some Important Polyatomic Molecules

Abstract

ABSTRACT newlineThe optimized structure and vibrational spectra of organic compounds like benzonitrile newlinegroup materials, Dyes, and amino acids were investigated experimentally and theoretically. newlineDensity functional theory calculations with different basis sets were used to determine newlineground state molecular geometries (bond lengths and bond angles and dihedral angels), Harmonic newlinevibrational frequencies, reduced masses, force constants, Infrared intensities, Raman newlineactivities, UltraViolet-visiblse (UV-Vis) spectra and Nuclear Magnetic Resonance (NMR) newlinechemical shifts of this compound using the Gaussian 09 and results were visualized using newlineGauss View and Gauss Sum programs. The Fourier Transformation Infrared (FT-IR) newlineand Fourier Transformation Raman (FT-Raman) spectra were compared with the experimental newlinevalues, which yield good agreement between the observed and calculated values. In newlinethe present study, the FT-IR and FT-Raman spectra of Non Linear Optical (NLO) activity newlinemolecules; derivatives of benzonitrile and benzophenone have been recorded in the range newlineof 4000-100cm-1. All the observed vibrational bands of the compounds are assigned to newlinethe various modes of vibrations and discussed in comparison with the structurally similar newlinemolecules and theoretical values. All the optimized structural parameters have been calculated newlineby Hatree-Fock (HF) and Density Functional Theory (DFT) methods with different newlinebasis sets. Optimized geometries of the molecules have been interpreted and compared with newlinethe reported experimental values. The harmonic and anharmonic vibrational wavenumbers, newlineIR intensities and Raman activities are calculated at the same theory levels used in geometry newlineoptimization. The calculated frequencies are scaled and compared with experimental newlinevalues. The scaled vibrational frequencies at B3LYP with higher order basis set seems to newlinecoincide with the experimentally observed values with acceptable deviations. The comparison newlineof experimental values in FT-IR and Raman with the simulated spectra with different newlinemethods provide importa