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  • American Institute of Physics (AIP)  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Electron-momentum-specific valence-shell electronic structures of cis-, trans-, and iso-butene by symmetric noncoplanar (e,2e) spectroscopy (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 4512-4519 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron-momentum-specific ionization energy (IE) spectra of cis-, trans-, and iso-butene were obtained from 8 to 44 eV ionization energy using noncoplanar symmetric (e,2e) spectroscopy and compared with the corresponding photoelectron spectra obtained using monochromated synchrotron radiation at 100 eV photon energy. In the independent particle picture, the intensity variation of a particular ionic state as a function of the electron momentum in an (e,2e) IE spectrum is characteristic of electron momentum density of the ionized orbital. Under favorable conditions, the (e,2e) IE spectra measured at two relative azimuthal angles (0° and 8°) can be used to provide a unique characterization of the dominant orbital composition of a particular ionic state. Together with ab initio calculations, these spectra have been used to clarify the nature of some of the ionic states found in the photoelectron spectroscopic studies. In particular, the presence of prominent many-body structures in the inner-valence region (≥20 eV) for all three butene isomers indicates the general breakdown of Koopmans' ionization picture in this region. The nature of these many-body states is inferred from their electron momentum dependence in the (e,2e) IE spectra and from recently published configuration-interaction calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465010
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  • 2
    Electronic Resource
    Electronic Resource
    Dissociation of doubly charged CH2=CD2 and CH2=CF2 in the region of valence shell photoexcitation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2908-2915 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dissociative double photoionization of 1,1-dideuteroethene (CH2=CD2) and 1,1-difluoroethene (CH2=CF2) has been studied using the photoion–photoion coincidence (PIPICO) technique and monochromated synchrotron radiation over the photon energy range of 37–85 eV. PIPICO branching ratios and threshold energies for dissociative double photoionization show two dominant exit channels of the doubly charged ions (i) central C=C bond cleavage to form CXm++CYn+ fragment ions at a threshold below 37 eV photon energy. The decomposition into H++C2HD2+, D++C2H2D+, and F++C2H2F+ are also appreciable, and (ii) the fragmentation into H+(D+ or F+)+CXm+ takes place at hν(approximately-greater-than)37 eV. Comparison of the present PIPICO branching ratios with the recent theoretical studies of the electronic states of the outer valence doubly charged ethene ion [Liegener, Chem. Phys. 92, 97 (1985) and Ohrendorf et al., J. Chem. Phys. 91, 1734 (1989)] indicates that double ionization involving release of one πC=C electron results in central C=C bond breakage, while that of two electrons of the σCH, σCC, and C 2s orbitals of ethene forms two smaller fragment ions of the H++CXm+type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464118
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  • 3
    Electronic Resource
    Electronic Resource
    A high sensitivity momentum dispersive multichannel electron momentum spectrometer for studies in experimental quantum chemistry (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 349-358 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and characterization of a high sensitivity multichannel momentum dispersive electron momentum spectrometer is reported. Electron pair coincidences are detected over a ±30° range of azimuthal angle at the exit slit of a cylindrical mirror analyzer configured to measure symmetric (θ=45°) noncoplanar (e,2e) scattering. A position sensitive microchannel plate/resistive anode encoder electron detector and a channeltron electron multiplier are employed in a novel multichannel coincidence detection system based upon detection of "pile-up'' of pairs of timing pulses from the detectors. Proof-of-concept results, exhibiting significantly higher coincidence count rates and statistical precision than have been previously observed in electron momentum spectroscopy, are presented for argon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145195
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of ion multiplier sensitivities as a function of ionic mass for use in quantitative mass spectrometry (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1140-1145 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental method has been developed for the determination of ion multiplier sensitivity to ions of different mass to charge ratio using the electron-ion coincidence technique of dipole (e,e+ion) spectroscopy. Time-of-flight mass spectra of each of the noble gas atoms He, Ne, Ar, Kr, and Xe are collected using the ion multiplier under investigation. In the present work we have determined relative efficiencies, at 7.5–8 keV ion impact energy, over the mass range 1–140 amu for two different large active area multipliers, a Johnston focused mesh multiplier and a microchannel-plate detector, both operated in the saturated pulse counting mode. Significant variations in detector sensitivity occur at low m/e values for both multipliers. The microchannel-plate detector shows a level response function above m/e=∼30, while the Johnston multiplier exhibits a slow decrease in sensitivity in the same mass range. The applicability of the measured response functions to the correction of molecular mass spectra and experimental photoion branching ratio data has been investigated. It appears that the detection efficiencies for atomic and polyatomic ions of the same m/e may be different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144107
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