Vesna Volovšek

DFT study of molecular structure and vibrations of 3-glycidoxypropyltrimethoxysilane.

Molecular structure and vibrational frequencies of 3-glycidoxypropyltrimethoxysilane (GPTMS) have been investigated by density functional theory (DFT) calculations using Beckes three-parameter exchange functional combined with Lee-Young-Parr correlation functional (B3-LYP) and standard basis set 6-311++G(d,p). In order to reveal some possible conformations of GPTMS, potential energy scan has been performed in three dihedral angles SiCCC, CCCO and OCCO. The calculations predict the existence of seven different conformations. Raman and IR spectra of liquid samples were recorded and complete assignment of the observed vibrational bands of GPTMS molecule has been proposed. Temperature dependence of Raman spectra between 203K and 293K was examined and vibrational modes characteristic for different conformers were detached.

Normal coordinate analysis of the halogenated disubstituted benzophenones

Abstract In a previous paper we performed systematic measurements of the 4,4′-disubstituted halogenated benzophenones 1 . A preliminary assignment of these spectra has been proposed. In the present paper we present the valence force field for this group of molecules as well as the final assignment based on the normal coordinate calculations.

Vibrational analysis of the benzophenone molecule and influence of its conformation on vibrational transitions

Abstract IR and Raman spectra of benzophenone and several of its isotopomers (d5−, dl0−, 13C- and 13Cd5-benzophenone) are the experimental basis for the normal coordinate analysis. The possibility of determining the conformation of the benzophenone molecule in solution from its vibrational spectrum is considered carefully. The dihedral angle between the central part of the molecule and the phenyl ring has been determined by fitting the calculated to the observed spectra. The final force field for the molecule was obtained for the dihedral angle of 35°.

Molecular vibrations and lattice dynamics of ortho-terphenyl

Infrared and Raman spectra of crystalline, melted and solvated ortho-terphenyl and its perdeuterated isotopomer, D14-ortho-tephenyl, have been recorded. Optimized geometries and vibrational frequencies were calculated by the semiempirical RHF/AM1 method and by DFT using the B3LYP functional and 6–31G(d) basis set. In both cases the lowest energy conformation is of C2 symmetry. With the scaled AM1 and B3LYP/6-31G(d) force fields the average error in reproducing the experimental molecular vibrational frequencies is 13cm−1 and 5cm−1, respectively. The AM1 potential energy surface for phenyl torsions was mapped on a 15° grid. The barrier to concerted internal rotation is estimated to lie between 3 kJ mol−1 and 6kJ mol−1. The calculations of the lattice dynamics at k = 0 in the low temperature fully ordered crystal phase of parent and deuterated ortho-terphenyl were performed with inclusion of six low lying intramolecular vibrations. The conformational change of the ortho-terphenyl molecule induced by crystal packing forces was taken into account by re-defining the unperturbed molecular vibrational state. Although an accurate assignment of lattice vibrations was not possible, the calculated spectra give quite a reasonable picture of the low frequency dynamics in crystalline ortho-terphenyl. The relevance of the results obtained to the glass forming property of ortho-terphenyl is discussed.

Temperature dependence and time evolution of the low frequency Raman spectrum of 4,4′-dibromobenzophenone

Abstract Temperature dependence of the low frequency Raman spectrum of 4,4′-dibromobenzophenone (DBrBP) crystal has been studied in the temperature interval from 340 K down to 10 K. At constant temperature of 10 K the laser power has been gradually increased from 3 mW to 200 mW. Time dependence of the spectra was also examined at the temperature of 10 K and laser power of 30 W.

Raman study of vibrational dynamics of aminopropylsilanetriol in gas phase

Raman spectrum of aminopropylsilanetriol (APST) in gas phase has been recorded at room temperature in macro chamber utilizing two-mirror technique over the sample tube. Unlike predominantly trans molecular conformation in condensed phase, the spectra of vapor show that the molecules are solely in gauche conformation with intramolecular hydrogen bond N···HO which reduces the molecular energy in respect to trans conformation by 0.152 eV. The assignment of the molecular spectra based on the DFT calculation is presented. The strong vibrational bands at 354 cm(-1), 588 cm(-1) and 3022 cm(-1) are proposed for verifying the existence of the ring like, hydrogen bonded structure. Special attention was devoted to the high frequency region, where hydrogen bond vibrations are coupled to stretchings of amino and silanol groups.