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Vibrational Assignment (vibrational + assignment)
Selected AbstractsIR and Raman Vibrational Assignments for Metal-free Phthalocyanine from Density Functional B3LYP/6-31G(d) MethodCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Xian-Xi Zhang Abstract Vibrational (IR and Raman) spectra for the metal-free phthalocyanine (H2Pc) have been comparatively investigated through experimental and theoretical methods. The frequencies and intensities were calculated at density functional B3LYP level using the 6-31G(d) basis set. The calculated vibrational frequencies were scaled by the factor 0.9613 and compared with the experimental result. In the IR spectrum, the characteristic IR band at 1008 cm,1 is interpreted as C,N (pyrrole) in-plane bending vibration, in contrast with the traditional assigned N,H in-plane or out-of-plane bending vibration. The band at 874 cm,1 is attributed to the isoindole deformation and aza vibration. In the Raman spectrum, the bands at 540. 566, 1310, 1340, 1425, 1448 and 1618 cm,1 are also re-interpreted. Assignments of vibrational bands in the IR and Raman spectra are given based on density functional calculations for the first time. The present work provides valuable information to the traditional empirical assignment and will be helpful for further investigation of the vibration spectra of phthalocyanine analogues and their metal complexes. [source] Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignment of dimethylsilylisocyanateJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2010Gamil A. Guirgis Abstract The Raman (3200-30 cm,1) and/or infrared spectra (3500 to 400 cm,1) of gaseous, liquid and solid dimethylsilylisocyanate, (CH3)2 Si(H)NCO, have been recorded. The MP2(full) calculations, employing a variety of basis sets with and without diffusion functions, have been used to predict the structural parameters, conformational stability, vibrational fundamental wavenumbers, Raman activities, depolarization values and infrared intensities to support the vibrational assignment. The low wavenumber Raman spectrum of the gas with a significant number of Q-branches for the SiNC(O) bend is consistent with an essentially linear SiNCO moiety. The ab initio calculations supported this conclusion as all possible orientations of the NCO moiety lead to nearly the same energy. This result is at variance with the conclusion from the electron diffraction study that the heavy atom skeleton was bent with an angle of 152(5)° with one stable cis conformer. It is believed that this reported angle difference from 180° is due to the shrinkage effect. The SiH distance of 1.486 Å has been obtained from the isolated SiH stretching wavenumber. From the adjustment of the ab initio MP2(full)/6-311+G(d,p) predicted structural parameters, a proposed structure is reported, which is expected to give rotational constants within a few megahertz of the actual ones. These experimental and theoretical results are compared with the corresponding quantities of similar molecules. Copyright © 2009 John Wiley & Sons, Ltd. [source] Vibrational spectroscopy investigation using density functional theory on 7-chloro-3-methyl-2H-1,2,4- benzothiadiazine 1,1-dioxideJOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2009S. Seshadri Abstract The solid phase Fourier transform infrared (FTIR) and Fourier transform (FT) Raman spectral analysis of 7-chloro-3-methyl-2H-1,2,4-benzothiadiazine 1,1-dioxide (diazoxide), an antihypertensive agent was carried out along with density functional computations. The optimized geometry, wavenumber and intensity of the vibrational bands of diazoxide were obtained by DFT-B3LYP level of theory with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The harmonic vibrational wavenumbers calculated have been compared with experimental FTIR and FT Raman spectra. The observed and the calculated wavenumbers are found to be in good agreement. The experimental spectra coincide satisfactorily with those of calculated spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] Surface-enhanced resonance Raman spectroscopy of rifamycins on silver nanoparticles: insight into their adsorption mechanismsJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2006Barry D. Howes Abstract Three widely used antibiotics from the rifamycin family, rifamycin SV sodium salt, rifampicin and rifaximin, have been characterized by resonance Raman (RR) and surface-enhanced resonance Raman spectroscopy (SERRS). SERRS spectra were recorded using aqueous silver colloidal dispersions prepared with two reducing agents, sodium borohydride and hydroxylamine hydrochloride, for a range of pH values to identify the SERRS-active substrate surface most suitable for each of the three antibiotics. Rifampicin was found to give intense SERRS signals only for the borohydride-reduced colloid and only at pH < 7.7, whereas the hydroxylamine HCl-reduced colloid was the best substrate for rifaximin, giving considerably more intense SERRS spectra than the borohydride colloid. SERRS spectra of rifaximin were observed only at pH < 7.0. It is proposed that the marked pH dependence of the SERRS enhancement results from a transition from an anionic to a neutral zwitterionic state. SERRS spectra of rifamycin SV were not observed for any experimental conditions. The antibiotics display remarkably contrasting SERRS behaviour, reflecting differences in the nature of the substituent groups on the chromophore ring. A vibrational assignment of the RR spectra and detailed comparison between the RR and SERRS data have given insight into the mechanism of adsorption of the antibiotics onto the Ag surface. Rifampicin and rifaximin adsorb adopting an approximately similar vertical orientation of the chromophore ring with respect to the surface; however, rifampicin adsorbs by direct chemical interaction with the Ag whereas rifaximin does not form a direct bond with the Ag surface. Copyright © 2006 John Wiley & Sons, Ltd. [source] Vibrational spectroscopic studies and DFT calculations of 4-fluoro- N -(2-hydroxy-4-nitrophenyl)benzamideJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2008L. Ushakumari Abstract Fourier transform infrared (FT-IR) and FT-Raman spectra of 4-fluoro- N -(2-hydroxy-4-nitrophenyl)benzamide were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red-shift of the NH-stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO-stretching mode gives the charge transfer interaction through a ,-conjugated path. Copyright © 2008 John Wiley & Sons, Ltd. [source] Raman and IR spectral studies of D -phenylglycinium perchlorateJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2002S. Ramaswamy The Raman and infrared spectra of D -phenylglycinium perchlorate were recorded at room temperature. Tentative vibrational assignments of the observed wavenumbers were made by comparison with the vibrational wavenumbers of glycine, phenylalanine and other similar compounds. Anions were found to coordinate through hydrogen bonding interactions to other ligands in the crystal, affecting the Td symmetry and thereby causing the degeneracies of several modes to be removed. The extensive intermolecular hydrogen bonding in the crystal leads to a shift of bands due to the stretching and bending modes of various functional groups. The broadening and appearance of multiple bands for the carbonyl stretching mode due to the resonance interaction is also discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||