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Journal of Raman Spectroscopy 04/2010; 42(1):108 - 116. · 3.09 Impact Factor
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ABSTRACT: Theoretical calculations on the molecular geometry and the vibrational spectrum of 4-hydroxybenzoic acid were carried out by the Density Functional Theory (DFT/B3LYP) method. In addition, IR and Raman spectra of the 4-hydroxybenzoic acid in solid phase were newly recorded using them in conjunction the experimental and theoretical data (including SQM calculations), a vibrational analysis of this molecular specie was accomplished and a reassignment of the normal modes corresponding to some spectral bands was proposed. The geometries of monomers and dimers in gas phase were optimized using the DFT B3LYP method with the 6-31G*, D95** and 6-311++G** basis sets. Also, both the vibrational spectra recorded and the results of the theoretical calculations show the presence of one stable conformer for the 4-hydroxybenzoic acid cyclic dimer. The B3LYP/6-31G* method was used to study the structure for cyclic dimer of 4-hydroxybenzoic acid and for a complete assignment our results were compared with results of the cyclic dimer of benzoic acid. A scaled quantum mechanical analysis was carried out to yield the best set of harmonic force constants. The formation of the hydrogen bond was investigated in terms of the charge density by the AIM program and by the NBO calculations.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 02/2010; 75(5):1422-34. · 2.10 Impact Factor
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Journal of Raman Spectroscopy 01/2008; 39:460-467. · 3.09 Impact Factor
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Chemical Physics 01/2007; 333:148-156. · 1.90 Impact Factor
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Vibrational Spectroscopy 01/2006; 40:1-9. · 1.65 Impact Factor
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Vibrational Spectroscopy 01/2006; 40:1-9. · 1.65 Impact Factor
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ABSTRACT: The joint experimental and theoretical study of the vibrational spectra of the molecular series (CH3)3SiX (with X=H, F and Br) is carried out. Data from newly recorded IR and Raman spectra for the bromo derivative, experimental data obtained previously for the remaining species, DFT theoretical calculations and the use of the SQMFF procedure have allowed us to propose common patterns and to unify criteria in their assignment. In addition, two sets of averaged scale factors for the B3LYP force field obtained with two different basis sets (6-31G* and DZP+diff) have been proposed for the common bulky moiety of that molecular series. These parameters were used successfully in order to reproduce the frequency of the bands assigned to the (CH3)3Si- group in the vibrational spectra of the corresponding silanolic and methoxy derivatives, i.e., trimethylsilanol and methoxytrimethylsilane, proving their transferability.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2006; 62(4-5):1058-69. · 2.10 Impact Factor
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ABSTRACT: The IR and Raman spectra of chlorotrimethylsilane (CTMS) were re-examined. Gas and liquid phase spectra were newly recorded and the analysis of the second derivatives of intensities in some complex spectral regions was carried out. The experimental study was combined with theoretical calculations at the B3LYP level with two different basis sets, i.e., 6-31G(*) and DZP+diff. The use of the SQM methodology, allowed us to review the assignment of the bands for nu(3) (methyl deformation), nu(5) (methyl rocking) and nu(8) (SiC deformation) normal modes of A(1) symmetry, as well as nu(16), nu(17) (methyl deformations) and nu(20) (methyl rocking) normal modes of E symmetry. The description of the asymmetric CH stretchings spectral region has been improved and, in addition, new values of vibrational frequencies were predicted for A(2) normal modes, inactive in both IR and Raman spectra. The equilibrium geometry parameters of CTMS obtained in this work at the MP2/DZP+diff level are closer to the experimental values than previous predictions.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 12/2005; 62(1-3):293-301. · 2.10 Impact Factor
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Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2005; 62:1058-1069. · 2.10 Impact Factor
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Chemical Physics Letters 01/2005; 412:359-364. · 2.34 Impact Factor
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Journal of Molecular Structure. 01/2005; 744-747:331-338.
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ABSTRACT: Gas and liquid phase infrared spectra and the liquid phase Raman spectrum of methoxytrimethylsilane (MTMS) have been newly recorded. Theoretical calculations at the B3LYP level, using two different basis sets, i.e. the standard 6-31G* and the Huzinaga–Dunning type DZP+diff, together with the application of SQMFF methodology have been used for the revision of the vibrational spectra of the title molecule, reproducing the whole IR and Raman spectral profiles. This has allowed us to propose the reassignment of some fundamental bands of its vibrational spectra, namely ν27, ν35, ν42, ν45, ν46 and ν48 and to compare them with those of previous assignments. The scale factors obtained for the trimethylsilyl group of this molecule along with those obtained by our group for a set of trimethylsylil derivatives will be used to get a specific set of averaged values suitable for the prediction of vibrational spectra of less stable species containing the Me3SiO group.
Journal of Molecular Structure.
