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  • Wiley-Blackwell  (91)
  • 1
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman (10-3500 cm-1) and infrared (50-3500 cm-1) spectra have been recorded for gaseous and solid ethyldimethylphosphine, CH3CH2P(CH3)2. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. From the fact that several distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phase with the gauche conformer being more stable and the only one present in the spectrum of the solid. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between the gauche and trans conformers was determined to be 134 ± 32 cm-1 (383 ± 92 cal mol-1). Relying on group frequencies and relative intensities of the infrared and Raman bands, and in some cases infrared band contours, a complete vibrational assignment is proposed for the gauche conformer. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution. The CH3-P torsions have been observed at 208 and 185 cm-1 in the gas phase and from these frequencies the periodic barriers to internal rotation have been calculated to be 905 ± 95 cm-1 (2.56 kcal mol-1). The CH3-C torsion was also observed in the gas phase at 217 cm-1 from which a periodic barrier of 1134 cm-1 (3.22 kcal mol-1) was calculated. The asymmetric torsional mode has been observed for the gauche conformer in both the infrared and Raman spectra of the gas at 91 cm-1 with evidence of ‘hot bands’ at lower frequencies. All of these results are compared with corresponding quantities for several other organophosphines.
    Additional Material: 4 Ill.
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  • 2
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman (3500-10 cm-1) and far-infrared (400-70 cm-1) spectra of solid 1,1-dicyanocyclopropane have been recorded. The molecular structure of cyclopropane, cyanocyclopropane and 1,1-dicyanocyclopropane have been calculated by ab initio methods at the 4-31G basis set level. The harmonic force fields for cyanocyclopropane and 1,1-dicyanocyclopropane have also been calculated using the same basis set. By the combination of experimental data and normal coordinate calculations with scaled ab initio force constants, the vibrational assignments for these two molecules have been revised. Discrepancies between the previously reported and present assignments are discussed. The molecular structures of cyanocyclopropane and 1,1-dicyanocyclopropane obtained in this work are compared with the molecular structure of cyclopropane.
    Additional Material: 4 Ill.
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  • 3
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature-dependent Raman spectra of crystalline uranyl nitrate hexahydrate, UO2(NO3)2 · 6H2O, are reported in the temperature range 15-290 K. A group theoretically consistent assignment of the bands in terms of UO22+, NO3- and H2O vibrations is proposed. The temperature-dependent studies of thermosensitive bands associated with these entities were used to study the previously reported phase transition at 140 ± 5 K and to detect another phase transition at 190 ± 5 K. The latter transition shows up prominently in the temperature-dependent fluorescence studies and is also accompanied by a sharp increase in the Rayleigh scattering. The transition at 190 ± 5 K is triggered by the dynamics of H2O-II and UO22+ whereas that at 140 ± 5 K is associated with the dynamics of H2O-II/NO3-. Both the transitions are of second order.
    Additional Material: 9 Ill.
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  • 4
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman (4000-10 cm-1) and infrared (4000-50 cm-1) spectra of gaseous and solid 1,1,1,3,3,3-hexafluoro-2-propanimine, (CF3)2 C=NH, were recorded. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. A complete vibrational assignment for the normal modes utilizing Cs symmetry is proposed based on band contours, depolarization values and group frequencies. The assignment is supported by a normal coordinate calculation utilizing a modified valence force field to calculate the frequencies and potential energy distribution of the normal modes. A CF3 torsional mode was observed in the Raman spectrum of the liquid at approximately 60 cm-1, from which a periodic barrier of 5.0 kcal mol-1 (1 kcal = 4.184 kJ) was calculated. The results are compared with similar data for some corresponding molecules.
    Additional Material: 4 Ill.
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  • 5
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman spectra of gaseous, liquid and solid 1, 1, 1-trifluoro-2-methoxypropane, CF3(CH3)CHOCH3, and the corresponding methoxy-d3 isotope, CF3(CH3)CHOCD3, together with the infrared spectra of the gases and solids were recorded from 3500 to 30 cm-1. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the amorphous and annealed solids indicates the predominance of two conformers in the fluid phases at ambient temperature. Owing to possible steric hindrance, it is suggested that the most stable conformer is the gauche-2 form, which has the methoxy group trans with respect to the carbon-carbon bond of the perfluoromethyl group. This conformer is the one present in the solid. The other conformer in appreciable abundance in the fluid states is probably the gauche-1 form, which has the methoxy group trans to the carbon-carbon bond of the methyl group. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between these conformers was determined to be 180 ± 100 cm-1 (515 ± 286 cal mol-1). The asymmetric torsional frequencies for the gauche-2 and gauche-1 conformers are 93 and 53 cm-1, respectively, and from these data and the enthalpy difference the values for the potential constants governing the internal rotation have been estimated. The normal modes have been assigned based on group frequencies, isotopic shifts, depolarization values and infrared band contours. The barrier to internal rotation of the methyl group is calculated to be 1275 cm-1 (3.65 kcal mol-1) from the torsional frequency of 234 cm-1 of the solid.
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  • 6
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman (3200 to 10 cm-1) and far-infrared (375 to 80 cm-1) spectra of gaseous bromocyclobutane, c-C4H7Br, have been recorded. A series of Q-branches observed in both of these spectra, beginning at 149 cm-1 with successive transitions falling to lower frequencies, have been assigned to the ring-puckering vibrations of both the low-energy equatorial and high-energy axial conformers. These data have been fit to an asymmetric potential function of the form V(cm-1) = (6.58 ± 0.21) × 105X4 - (3.27 ± 0.04) × 104X2 × (4.59 ± 0.19) × 104X3 with a reduced mass of 214 amu. Utilizing this potential, the difference between the puckering angles for the two conformers is calculated to be 6°, with the equatorial conformer having the larger value of 20°. Also from this potential function, the energy difference between the equatorial and axial forms is found to be 361 ± 20 cm-1 (1.03 kcal mol-1), with a barrier of 636 ± 20 cm-1 (1.82 kcal mol-1) to interconversion. Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (297 ± 27 cm-1) and gas (∼ 350 cm-1) from relative intensities of a pair of Raman lines over 90 and 58 °C temperature ranges respectively. These results are compared to the corresponding quantities for some similar molecules.
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  • 7
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Laser-excited emission from YBa2Cu3O7-δ with 7.5% dysprosium nominally subsituted in place of yttrium is presented in the range 13 000-23 000 cm-1. In addition to the reported Raman lines in the Cu—O stretching region, a number of other spectral features were observed. These include a discrete luminescence with lines at 14 400 and 14 425 cm-1 and a broad emission with its peak position and band width varying with excitation wavelength. Additionally, an anti-Stokes scattering, which has no apparent counterpart in the Stokes region, was observed. These observations may be of significance in the elucidation of the mechanism of high-temperature superconductivity.
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  • 8
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman (4000-10 cm-1) and infrared (4000-80 cm-1) spectra of methyl nitrite, CH3ONO, and methyl nitrite-d3 were recorded in the gas and solid phases. Additionally, the Raman spectra of the pure liquids were recorded and qualitative depolarization values were obtained. Support for the interpretation of these new data is provided by ab initio calculations using the 6-31G* basis set. Complete equilibrium geometries have been determined for both conformers, as well as structures for every 30° rotation about the N—O bond. These calculations give a cis/trans barrier of 4015 cm-1 (11.5 kcal mol-1), a trans/cis barrier of 3504 cm-1 (10.0 kcal mol-1) and an enthalpy difference between conformers of 511 cm-1 (1.5 kcal mol-1) with the cis form being more stable. From a variable temperature Raman study of liquid methyl nitrite-d3 it is concluded that the cis form is also more stable in this phase with an enthalpy difference between conformers of 262 ± 3 cm-1 (750 ± 9 cal mol-1). A complete assignment of the vibrational fundamentals is proposed based on band contours, depolarization values, group frequencies and shift factors for the two isotopomers. These assignments are supported by normal coordinate analyses using the ab initio force fields to obtain frequencies and potential energy distributions for both conformers.
    Additional Material: 9 Ill.
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  • 9
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thin sputtered films of the high-Tc material YBa2Cu3O7-Δ were investigated using 180° back-scattering geometry with Fourier transform (FT) Raman spectroscopy. It is established that the main bands in the spectra of a YBa2Cu3O7-Δ film on strontium titanate substrate exhibit similarity with those obtained for oriented untwinned crystallites of the superconductor having their c-axis perpendicular to the surface of the substrate. No degradation or excessive heating of the film was observed with 1.064 μm excitation for low laser powers. The film on a magnesium oxide substrate gives unique evidence of the isolated strong, featureless, almost flat continuum, producing a broad maximum near the region of the antiphase axial bending O(2)—Cu(2)—O(3) motions of planar oxygens at very low excitation energy. This appears to be the first application of FT-Raman spectroscopy using near-infrared excitation (1.064 μm) to the field of high-temperature superconducting films and their detailed characterization.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 22 (1991), S. 727-727 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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