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  • Analytical Chemistry and Spectroscopy  (3)
  • 71.45.Gm  (1)
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Keywords
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 25 (1993), S. 181-184 
    ISSN: 1434-6079
    Keywords: 42.65.An ; 36.40.+d ; 71.45.Gm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Motivated by a discrepancy of five orders of magnitude between three different hyperpolarizability measurements on the C60 fullerene, we calculated the optical response of this cluster using a tight-binding Hamiltonian and compared the results to those for a benzene molecule. Our Hamiltonian reproduces the linear polarizability and hyperpolarizability of benzene reasonably well. For C60, our calculations of the bare polarizability agree only with two of the optical response measurements and indicate that the corresponding linear and nonlinear response of C60 is much larger than that of C6H6. We find that screening effects decrease this difference strongly, and also reduce the calculated hyperpolarizability of C60 to a value which is two orders of magnitude below the favored measurements.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 920-928 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Deviations of electrode shapes from pure quadrupole systems result in the superposition of higher multipole fields onto the quadrupole field. Non-linear resonances are generated due to these higher multipole fields. These non-linear resonances can be thought of as internal resonances, which must fulfil appropriate conditions. In this paper, general non-linear resonance conditions for a time-variable, three-dimensional, non-linear quadrupole system are derived, using previously described methods. The occurrence of resonances depends on the electrode shapes of the non-linear quadrupole systems which control the weight factors of the higher multipole fields. With special electrode shapes, for example shapes with symmetry, the resonance effects are reduced. Different higher multipoles (for example, octopoles and dodecapoles) generate non-linear resonances which fulfil different and/or the same resonance conditions. Each resonance condition can be described by resonance lines within the stable regions of the stability diagram. Resonant ion motion possesses the characteristic that groups of ion frequencies are simultaneously resonant. These properties are analyzed and corresponding results are given.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 21 (1990), S. 435-440 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Substantial saturation effects are noted for resonance Raman (RR) bands of the aromatic residues in cytochrome c (excited at 230 nm) with an H2 Raman-shifted YAG or a frequency-doubled excimer-pumped dye laser. At a given average power, saturation is much lower for excimer than for YAG excitation because of the longer pulse and higher repetition rate of the excimer laser. The signal quality at low average power is significantly higher for the excimer-excited spectra. Ultraviolet RR cross-sections have been redetermined for aqueous phenylalanine, tyrosine and tryptophan at a series of wavelengths from 240 to 192 nm. The excimer laser was used at 209 nm and longer wavelengths, and in addition deconvolution techniques were applied to better define the individual RR bands. These improvements led to quantitative changes in the cross-section values from those reported previously, but the interpretation of the excitation profiles in terms of excited-state properties of the aromatic residues remains unchanged.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 26 (1995), S. 959-962 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The observation of surface-enhanced Raman scatterings (SERS) from CO2 molecules dissolved in aqueous solutions of silver and gold colloids measured with 850 nm near-IR excitation is reported. Different types of surface enhancement and surface-enhanced Raman spectra were observed. The SERS spectrum of CO2 on colloidal gold is in good agreement with the spectrum of CO2 dissolved in water. Two different types of SERS spectra were found for CO2 on colloidal silver. They can be assigned to physisorbed and/or weakly chemisorbed CO2 molecules and to strongly bonded CO2 - negatively charged surface radicals, respectively. The enhancement factor for the stretching mode of carbon dioxide is estimated to be of the order of 102-104, depending on the kinds of metal and types of adsorption, which demonstrates that SERS on colloidal silver or gold particles in solution offers possibilities for detecting CO2 dissolved in liquids at low concentrations.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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