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  • 1
    Electronic Resource
    Electronic Resource
    High Rydberg states of methyl iodide perturbed by nitrogen: A mutual cancellation of shift terms (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 7885-7889 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dependence of the positions of both prethreshold and autoionizing high Rydberg states of CH3I on the density ρ of the perturber N2 was measured at room temperature, using synchrotron radiation. Up to ρ=2.2×1020 cm−3 no pressure shift was observed, showing that the scattering shift by the valence electron is compensated by the polarization shift due to the core. From the results, the value A=(1.9±0.3)×10−9 cm was found for the scattering length, in good accord with previous pressure shift and swarm results. The wide range of useful applications of the photocurrent excitation spectra to the study of perturbed transitions is stressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462341
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  • 2
    Electronic Resource
    Electronic Resource
    Electron scattering in dense CO2 gas: Photoionization spectra of CH3I perturbed by CO2 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 4070-4073 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A photoionization study of CH3I in the presence of dense CO2 (density range: 1.6–10.0×1019 cm−3 ) revealed the prethreshold 2E3/2 Rydberg transitions of methyl iodide perturbed by CO2. From the measured pressure shift of the nd Rydbergs (n=11,12,13,14) the scattering length of CO2 was deduced as A=−0.224 nm, in accord with cross-section data. The vibrational structure of CO2 above 9.54 eV was found to be superimposed on the CH3I absorber photoionization spectrum, yielding a spectrum more detailed than absorption spectra of pure CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460762
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  • 3
    Electronic Resource
    Electronic Resource
    Autoionization spectra of CH3I in dense gaseous methane, ethane, and propane observed by photoconduction (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1820-1824 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The influence of light alkane perturbers (up to densities 5×1020 cm−3 for methane and ethane and 2×1020 cm−3 for propane, respectively) on the autoionization spectrum of CH3I nd'(2E1/2) Rydberg series was investigated by photoconductivity excitation spectroscopy. In the experiments, we recorded photocurrents due to electronic transitions from the absorber molecule to the conduction state of each perturber. The absorption maxima of the perturbed autoionization Rydberg states appeared as maxima in the photocurrent spectrum. The asymptotic pressure shift of the Rydberg lines equals the shift of the second vertical ionization potential I(2E1/2) of the perturbed absorber. The energy shift also provides the electron scattering length A in methane, ethane, and propane. The data obtained are compared with results in the literature on photoinjection, electron beam, and swarm experiments in pure alkanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459956
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  • 4
    Electronic Resource
    Electronic Resource
    Photocurrent excitation spectra of methyl iodide/methane fluid mixtures (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 187-193 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Impurity photocurrents of fluid CH4:CH3I were studied in the region of the (2E1/2)nd Rydberg series of CH3I and also beyond the 2E1/2 ionization potential up to the LiF cutoff. In the gas, a step-like rise of the photocurrent was observed at a photon energy somewhat lower (by about 20 meV) than the 2E1/2 ionization potential, indicating that high members of the (2E1/2)nd Rydberg series of methyl iodide can be ionized by further processes besides the well-known autoionization into the 2E3/2 continuum. At the high-energy side of the 2E1/2 limit further peaks appear, corresponding to simultaneous excitation of (2E1/2)nd Rydberg states and one or two quanta of the ν2(a1) vibration of CH3I. In the photon energy region of 10.8–11.8 eV a series of at least eight peaks were observed, due to excitation of vibronic levels of the Jahn–Teller split 4s Rydberg state of methane. The value of the adiabatic ionization potential 2E3/2 of CH3I in liquid CH4 near the critical point was found to be 8.30 eV, while in neat dilute CH3I gas it is 9.48 eV. The overall variation of 2E3/2 in the liquid phase (from 190 to 132 K, 6.4×1021 to 1.5×1022 cm−3) is 70 meV. In the densest (and coolest) liquid samples studied a series of peaks, with intervals of ≈60 meV appeared in the photon energy range 8.37〈hν〈8.5 eV on top of the continuous background.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468168
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of methane on photocurrents generated by exciting xenon below its first ionization potential (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4628-4634 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photocurrent excitation spectra of xenon and of the xenon–methane absorber–perturber system were studied in cells equipped with LiF windows cooled to ≈−30 °C. The cooling was needed to shift the LiF cutoff so as to enable measurements at photon energies up to the first ionization potential of Xe (12.13 eV). The spectra observed in methane–xenon mixtures were essentially similar to those in neat xenon, demonstrating that the Hornbeck–Molnar process (excitation of a xenon atom–excimer formation–ionization of an excimer) is feasible even in the presence of the molecular perturber CH4 at pressures up to ≈ 105 Pa. The primary effect of CH4 is to decrease the photocurrent, since photons in the energy range in question are absorbed by the methane molecules as well, without photoionizing them. The dependence of the current on methane concentration showed that the above mechanism is not the only one by which methane quenches the current. Moreover, the degree of quenching of the current by methane is dependent on the photon energy. The analysis of this dependence led to the assumption that an excited xenon atom and a methane molecule may form an excimer. Previous results on the Ar:Xe and Kr:Xe systems support this assumption. Peak inversions observed at high pressures in neat xenon, but absent in the CH4:Xe system, are discussed on the basis of prevailing models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467451
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  • 6
    Electronic Resource
    Electronic Resource
    On the inapplicability of the layer-transposition mechanism to polytype formation in ZnS (1973)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 6 (1973), S. 292-293 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The frequency distribution of the relative lengths of cubic stacking sequences in vapour-phase-grown ZnS polytypes is presented. It is shown that this distribution conflicts with the correlation between atomic structures and stacking-fault energy expected on the assumption of a layer-transposition mechanism for polytype formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188987300871X
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  • 7
    Electronic Resource
    Electronic Resource
    The determination of crystallite dimensions using synchrotron-radiation X-ray diffraction photographs (1979)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 12 (1979), S. 525-530 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Synchrotron-radiation Laue patterns give valuable information on the sizes and shapes of grains in a polycrystalline material even if these are too small for synchrotron topography. A calculation, based on kinematic theory, is presented for the radial and lateral broadening of the diffraction spots obtained with white radiation. The most conspicuous broadening is to be expected when the dimensions of the reflecting planes are small and not their number; this is at variance with the conditions leading to broadening with conventional monochromatic methods. Quantitative assessment of the crystal dimensions is possible if auxiliary spectral information is obtained by using selectively absorbing filters. The theory was applied to the analysis of Laue photographs of xenon and krypton crystallites condensed on a cooled beryllium substrate. Crystal dimension down to a few nanometers could be determined. The method is, in principle, applicable to the determination of the grain size and shape distribution of fine-grained polycrystalline samples of any material. Changes during crystallization and recrystallization can be easily followed by virtue of the simple experimental set-up and short exposure times involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889879013200
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  • 8
    Electronic Resource
    Electronic Resource
    New families of ZnS polytypes (1969)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 1581-1586 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567740869004353
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of the cyclicity of polytypes (1970)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 26 (1970), S. 24-28 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567740870001863
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  • 10
    Electronic Resource
    Electronic Resource
    The family 24L of ZnS polytypes (1971)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 27 (1971), S. 378-381 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567740871002255
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