No abstract

The molecular geometry, the normal mode frequencies and corresponding vibrational assignments, natural bond orbital analysis and the HOMO-LUMO analysis of 7-Amino-2,4-dimethylquinolinium formate in the ground state were performed by B3LYP levels of theory using the 6-31G(d) basis set. The optimised bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of the title compound which is calculated by DFT method, reproduces vibrational wave numbers and intensities with an accuracy which allows reliable vibrational assignments. The possibility of N-H⋯O hydrogen bonding was identified using NBO analysis. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction.

No abstract

Vibrational spectral analysis of the hydrogen-bonded nonlinear optical (NLO) material p-bromo acetanilide (PBA) was carried out using NIR-FT-Raman and FT-IR spectroscopy. Ab initio molecular orbital computations were performed at HF/6-31G (d) level to derive equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The lowering of the imino stretching wavenumbers suggests the existence of strong intermolecular N-H· · ·O hydrogen bonding, which was substantiated by the natural bond orbital (NBO) analysis. The vibrational spectra confirm that the charge-transfer interaction between the -NHCOCH 3 group and -Br through phenyl ring is responsible for simultaneous strong IR and Raman activation of the ring mode 8a. Vibrational analysis indicates that the lowering of stretching wavenumbers of methyl group due to electronic effects simultaneously caused by induction and hyperconjugation is due to the presence of the oxygen atom. The presence of blue-shifting H-bonds of CH stretching wavenumbers, simultaneous activation of carbonyl stretching mode, the strong activity of low-wavenumber H-bond stretching vibrations and the role of intramolecular charge transfer in making the molecule NLO active have been analyzed on the basis of the vibrational spectral features.

No abstract

Single crystals of (S)-phenylsuccinic acid (SPSA) were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. The density functional theoretical (DFT) computations were also performed at the B3LYP/6-311G(d, p) level to derive the equilibrium geometry, vibrational wavenumbers and intensities. Vibrational spectral investigation confirmed the formation of cyclic dimers in the crystal, with the carboxyl groups of each acid molecule being hydrogen bonded to those of the adjacent molecules. The Raman vibrational wavenumbers of the adsorption geometry of (S)-phenylsuccinic acid (SPSA) on a silver surface have been simulated using DFT-B3PW91 with lanl2dz basis set and it compared with the experimental spectrum. The large enhancement of in-plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in an 'at least vertical' or slightly tilted orientation, with the ring perpendicular to the silver surface. The calculated vibrational spectra are in agreement with experimental values confirming the validity of the proposed adsorption configurations.

No abstract

No abstract