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  • Chemistry  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Depolarization dispersion curves of some Raman fundamentals in ferrocytochrome c and oxyhaemoglobinIssued as NRCC No. 28298. (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 19 (1988), S. 23-32 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Depolarization dispersion curves and Raman excitation profiles of three fundamentals in ferrocytochrome c (1585, 1312 and 1363 cm-1) and oxyhaemoglobin (1583, 1376 and 1638 cm-1) are calculated togther with the corresponding absorption spectra in the region of 16000-23000 cm-1. A four-orbital model with two-electron interaction term and vibronic coupling terms for the a1g, a2g, b1g and b2g vibrations is used in two-mode calculations. It is shown that the observed depolarization dispersion curves indicate the presence of symmetry-breaking A2g and B1g electronic perturbations in ferrocytochrome c and of a B2g off-diagonal electronic perturbation in oxyhaemoglobin. These electronic perturbations lower the D4h symmetry of the porphyrin ring. It is also demonstrated that smaller vibronic perturbations become active in these molecules at lower symmetry. These vibronic perturbations result mainly from the symmetry-forbidden (D4h group) linear dependence of the nuclear potential energy in the Q and B states and of the two-electron interaction term on non-totally symmetric vibrational coordinates.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250190105
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  • 2
    Electronic Resource
    Electronic Resource
    Totally symmetric progressions in resonance Raman spectra and excitation profilesIssued as NRCC No. 19434. (1981)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 11 (1981), S. 369-374 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intensity distribution in totally symmetric progressions in resonance Raman spectra and excitation profiles is re-examined with the aim of removing remaining discrepancies between theory and experiment. New low-temperature intensity data are reported on the permanganate ion in a perchlorate pellet. New calculations are reported on this ion as well as on β-carotene in carbon disulfide solution. The main conclusion is that a careful consideration of lineshapes and line broadening mechanisms is required and that intensities in resonance Raman spectra must not automatically be equated in peak heights. It is shown that the remaining discrepancies in MnO4- are due to the neglect of the nontotally symmetric modes which are Jahn-Teller active and affect the totally symmetric excitation profiles through a breakdown of the Condon approximation. The theoretical model used to analyze β-carotene is improved by the introduction of Gaussian lineshapes associated with inhomogeneous line broadening.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250110515
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Theory of resonance Raman scattering by molecules subject to twisting with an application to ethyleneIssued as NRCC NO. 31001. (1990)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 21 (1990), S. 263-271 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Model calculations are reported on molecules such as ethylene that twist on electronic excitation. Resonance Raman spectra and excitation profiles are calculated for several pairs of torsional potentials. For a 90° twist, the resonance Raman spectra show double-quantum torsional progressions that tend to be very long for resonance in the region of strong absorption. The Raman excitation profiles of the torsional-mode bands resemble the absorption spectrum in that most of the intensity is found in the region of near-vertical transitions, where the upper-state torsional levels change from vibrational to rotational. This picture remains valid if the upper state has minima at angles other than 90° relative to the ground-state minimum, provided that the point group symmetry of the molecule is not lower than D2 at these points; this is the case for ethylene. If, however, the minimum corresponds to a lower point group, as for asymmetrically substituted ethylenes, Raman transitions involving an odd number of quanta become allowed. For very small angles of twist (≲ 15°) such systems resemble displaced harmonic oscillators. These results are compared with recently reported resonance Raman spectra in the UV absorption region of ethylene where both π→π* and Rydberg transitions are active. The analysis suggests a new potential for torsion in the first Rydberg state.
    Additional Material: 25 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250210409
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  • 4
    Electronic Resource
    Electronic Resource
    Depolarization dispersion of a fundamental line of a totally symmetric vibration in resonance Raman scattering (1976)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 5 (1976), S. 181-192 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibronic coupling of the Herzberg-Teller type is discussed as a possible source of the depolarization dispersion of a fundamental line of a totally symmetric vibration in resonance Raman scattering (RRS). Two cases are discussed separately. The first case concerns RRS from an electronic state that borrows part of its intensity from a non-overlapping electronic state of different symmetry. In this case the depolarization ratio of the fundamental line for right angle scattering linearly polarized light can vary between the limits 1/8 and 3/4. The second case arises when part of the intensity is borrowed from an electronic state of the same symmetry but with a transition moment non-parallel to that of the resonant state. Such a situation can occur in molecules with a symmetry corresponding to one of the following point groups: C1, Ci, C2, Cs, C1h, C2h, S2. In this situation the depolarization ratio ρl can vary between the limits 1/8 and. In both cases the amplitude of the variations of ρl depends on the damping constant. In the second case the value of the displacement parameter of a totally symmetric mode has a major influence on the range of change of ρl. Both cases show prominent resonance-antiresonance coincidences between depolarization dispersions and excitation profiles, which has been previously predicted for non-totally symmetric modes, and for molecular dimers. It is pointed out that the depolarization ratio in the preresonance region is very sensitive to vibronic coupling and can serve as a probe of such coupling.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250050209
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    The analysis of unresolved Raman excitation profiles. 1 - Totally symmetric vibrations with applications to ruthenium red and zirconium trisulfideIssued as NRCC No. 20256. (1982)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 13 (1982), S. 78-90 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The problems involved in the analysis of unresolved Raman excitation profiles are studied theoretically. The aim of such an analysis is to identify vibrational parameters of the resonant state and possibly other states involved in the scattering. For totally symmetric modes, discussed in this paper, the most important of these parameters are the displacements of the equilibrium positions, the problem being to separate these parameters from vibronic line broadening. It is shown how this can be done for systems of several modes and several interfering electronically excited states by model calculations based on a multimode approach. The effect of coupling with solvent modes on vibronic lineshapes is considered explicitly. Some reported analyses based on the independent-oscillator approach are criticized for their lack of internal consistency or their use of unacceptable parameter values. It is demonstrated that these analyses can be improved by taking multimode effects into account. For cases where the full N-mode problem is too difficult to handle directly, a method based on interrelated n〈N-mode calculations is developed. Two examples are treated in detail, namely ruthenium red and ZrS3. For both, sets of displacement parameters are derived from the unresolved profiles. A condition for the feasibility of such an analysis is the availability of excitation profiles for all Raman active fundamentals and one or more overtones or combination bands.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250130114
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