E.L. Varetti

The force constants in the isoelectronic series CF3SO2X (X = F, OH, NH2, CH3): a study based on DFT calculations and experimental data

Abstract Density functional theory calculations at the B3LYP/6-31G(d,p) level of theory were performed on the members of the isoelectronic series CF 3 SO 2 X (X=F, OH, NH 2 , CH 3 ), in order to obtain the optimized geometric parameters and conformations for the four molecules, as well as the wavenumbers corresponding to the normal modes of vibration and the associated force constants. The original force field was transformed to local symmetry coordinates and scaled to reproduce the experimental wavenumbers. The trends observed in geometrical parameters and force constants along the isoelectronic series could be explained making use of the calculated atomic charges.

TGA-DTA, infrared and x-ray powder diffraction studies on strontium nitroprusside and its hydrates

Abstract Dehydration data for the tetra-, di- and monohydrate of strontium nitroprusside and the vibrational behaviour of the water molecules in normal and deuterated samples agree with crystal data previously reported (for the di- and tetrahydrate as single crystals) and in this paper (monohydrate as a powder). Four distinct types of water molecules are present in the three hydrates with one type (oxygen bonded to Sr 2+ ) in common. Other types are a non hydrogen-bonded molecule (dihydrate), a molecule bonded by a single hydrogen atom to the nitrogen atom of a cyanide group and a set of two molecules similarly bonded to the oxygen atom of the previous type (tetrahydrate). The spatial orientation of the NO groups of the nitroprusside ions in the tetrahydrate is confirmed by the observed dichroism of the corresponding stretching band.

Infrared evidence of NO linkage photoisomerization in Na2[Fe(CN)5NO]·2H2O at low temperature: experimental and theoretical (DFT) isotopic shifts from 15N(O), 18O and 54Fe species

Infrared spectra of the metastable state I (MSI) of normal and 15NO, N18O and 54Fe isotopically substituted sodium nitroprusside dihydrate (Na2[Fe(CN)5NO].2H2O) have been obtained at 77 K. A comparison of the isotopic shifts measured for the vibrational modes of the FeXY (XY = NO or ON) moiety with those calculated by means of quantum chemistry (DFT) procedures supports the linear Fe-O = N arrangement for the MSI state.

Raman or Fluorescence Spectra? About the Use of FT-Raman Techniques on Inorganic Compounds:

The use of interferometric instruments and excitation of samples with near-infrared light to obtain Raman spectra has established itself as a very useful technique. The main advantage, besides the relative simplicity of this approach, is the absence of the intense fluorescence background very often encountered with dispersive instruments when one is using visible light for excitation, mainly for organic samples.

Experimental and theoretical vibrational study of 2,2,2-trifluoroethyl trifluoromethanesulfonate, CF3SO2OCH2CF3

The infrared spectra of 2,2,2-trifluoroethyl trifluoromethanesulfonate (CF3SO2OCH2CF3) were obtained in the gaseous, liquid and solid states as well as the Raman spectrum of the liquid. Quantum chemistry calculations using the density functional theory were used to predict the most stable geometry and conformation of the studied molecule. Subsequently, the harmonic vibrational frequencies and force field were calculated. An assignment of the observed spectral features made after comparison with the related molecules and with the predicted frequencies was used as the basis of a scaling of the original force field in order to reproduce as well as possible the experimental frequencies. With this purpose a set of scale factors was calculated by a least square procedure, leading to a final root mean square deviation (RMSD) of 9.7 cm(-1).

Experimental and theoretical vibrational study of silyl trifluoromethanesulfonate, CF3SO2OSiH3

Infrared and Raman spectra were obtained for liquid silyl trifluoromethanesulfonate, a silylating agent of limited stability. The molecular geometry was optimized by means of density functional theory and Möller-Plesset second order perturbation theory methods, using different basis sets. The optimized structure presents a gauche conformation, similar to that adopted by methyl trifluoromethanesulfonate, which was determined experimentally a short time ago. The wavenumbers for the normal modes of vibration and the corresponding force constants were also calculated, facilitating the interpretation of the vibrational data. The harmonic force constants given by theory were scaled to reproduce adequately the experimental wavenumbers.

Theoretical study of the structure and vibrational spectra of VO2X2− (X=F, Cl, Br, I) anions

Abstract We have carried out a structural and vibrational theoretical study for the four members of the series VO 2 X 2 − (X=F, Cl, Br, I). In order to assess the behaviour of such theoretical calculations (ab initio and DFT) we have made a comparative work for the fluorine and chlorine derivatives, for which vibrational data exist, to evaluate not only the best level of theory but also the best basis set to be used to reproduce the experimental wavenumbers. The results were then used to predict the vibrational spectra and molecular geometry of the other members of the series, for which there are no experimental data. The theoretical vibrational calculations allowed us to obtain a set of scaled force constants fitting the observed wavenumbers.

The IR spectra of perfluoromethyl perfluoroacetate and perfluoromethyl carbonate

Abstract The infrared spectra of perfluoromethyl perfluoroacetate and perfluoromethyl carbonate in the gaseous (4000-400 cm−1) and solid phases (2000-600 cm−1) are presented and interpreted. A band assignment has been attempted for the normal vibrational modes in the experimental spectral range.

A theoretical study of the vibrational properties of trifluoromethanol and the trifluoromethyl hypohalites, CF3OX (X=H, F, Cl, Br)

Abstract The vibrational properties of the CF 3 OX (X=F, Cl, Br, H) series of molecules were studied by means of density functional theory techniques. After obtaining the optimized geometrical parameters and conformations, the wavenumbers corresponding to the normal modes of vibration and the associated force constants were calculated. The original force fields in cartesian coordinates were transformed to local symmetry coordinates and subsequently scaled to reproduce the experimental wavenumbers. Some trends observed in the experimental data could be explained on the basis of the calculated atomic charges.

The polarized infrared and Raman spectra of crystalline ammonium trifluoromethanesulphonate

Abstract The infrared and Raman spectra of NH 4 CF 3 SO 3 were obtained and analysed and an assignment was proposed for the observed bands. The assignment of some anion bands was supported by means of the polarized spectra of monocrystals. The fundamental frequencies of the anion were used for a normal coordinate calculation.