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  • 1
    Electronic Resource
    Electronic Resource
    Site-selective fragmentation in core-excited bromo-chloro-alkanes [Br(CH2)nCl] (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 3742-3749 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report strong site-selective ionic fragmentation of the core-excited bromo-chloro-alkanes [Br(CH2)nCl] (n=1,...,3), using time-of-flight mass spectrometry in the multicoincidence mode and monochromatized synchrotron radiation to excite the vicinity of the bromine 3d (65–150 eV) and chlorine 2p edge (150–220 eV), respectively. We observe strong differences between the fragmentation after excitation of the two edges, where for all three molecules the bond between the excited halogen atom and the rest of the molecule is broken preferentially. This site selectivity is discussed in terms of a fast two- and three-body fragmentation which takes place after the primary Auger decay of the core vacancy but on the same time scale as further autoionization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467558
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  • 2
    Electronic Resource
    Electronic Resource
    Satellites and double ionization continua in the CS2 photoelectron spectrum (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2536-2548 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The CS+2 valence satellites have been studied with photoelectron spectroscopy using synchrotron radiation in the 35–75 eV photon energy range. Partial cross sections (σ) and asymmetry parameters (β) for most bands have been measured as a function of photon energy. Below 28 eV binding energy, the symmetry of satellite bands has been identified on the basis of their β value and a comparison between experimental photoelectron spectra and new ab initio SCF-CI calculations of CS+2 corrected for transition moments. For the bands with binding energies above 28 eV no configuration interactions states of CS+2 are predicted with significant intensity. We suggest that they originate from the opening of direct double ionization continua. This is supported by the similarity of their cross sections with the total double ionization one.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453093
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental and theoretical study of configuration interaction states of CO+2 (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2050-2061 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Configuration interaction states of CO+2 have been observed as satellites in a high resolution photoelectron spectrum of CO2 using an angle resolved electron spectrometer and far UV synchrotron radiation in the 30–55 eV photon energy range. Ten satellites have been identified in the 22–40 eV binding energy region and classified as the result of outer and inner valence ionization processes on the basis of their asymmetry parameter ( β) values. Theoretical calculations of configuration interaction states of CO+2 using an ab-initio SCF-CI method show that three-hole-two-particle excited configurations are necessary to explain the line positions and intensities. The calculated satellite spectrum, corrected for transition moments at 45 and 1254 eV, shows an excellent agreement with experiment and allows assignments of both outer and inner valence satellite lines, with Πg, Πu, Σ+g, and Σ+u symmetries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450413
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  • 4
    Electronic Resource
    Electronic Resource
    Autoionization observed in the CO+ (A 2Π–X 2Σ+) and (B 2Σ+–X 2Σ+) fluorescence excitation spectra (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1231-1236 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The CO+ (A 2Π–X 2Σ+) and (B 2Σ+–X 2Σ+) fluorescence excitation spectra (FES) using VUV synchrotron radiation, have been measured from 16 to 38 eV excitation energy. Total photoionization cross section has also been measured from 17 to 20 eV for comparison. Sharp ionization onsets typical of direct ionization process are observed for both A 2Π and B 2Σ+ thresholds. New autoionization structures have been observed above 20 eV besides the broad shape resonance located at 32 eV in the (B–X) FES. Sharp structures observed above the A 2Π (v=0) threshold are interpreted in terms of electronically induced vibrational autoionization. Branching ratios for electronic autoionization of four Ryberg series converging to B into the CO+ A and X states have been measured. Those states decay preferentially into the CO+ A 2Π state as opposed to X 2Σ+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448442
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  • 5
    Electronic Resource
    Electronic Resource
    Angle resolved photoelectron study of resonances near the Si 2p edge of the Si(CH3)4 molecule (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 492-498 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoelectron spectra of tetramethylsilane, were measured at selected photon energies in the vicinity of the Si 2p edge, using synchrotron radiation. In addition to known valence and core Si 2p bands, three LVV Auger lines (69, 76, and 80 eV electron energy) were observed for the first time. Partial and differential cross sections for the Si 2p band and two of the Auger lines have been measured at several photon energies from the Si 2p onset up to 135 eV. An intense resonance is evident in the Si 2p continuum as well as in the LVV Auger decay channels. Its position, right above threshold, accounts for only a part of the absorption feature. Another maximum, already seen in absorption around 124 eV, may be a shape resonance associated with the Si 2p continuum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449511
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical and experimental studies of the triatomic doubly charged ions CO2+2, OCS2+, and CS2+2 (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1259-1269 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The term schemes of the doubly charged ions CO2+2, OCS2+, and CS2+2 have been calculated by the CIPSI method using a new and economical basis set of polarized atomic orbitals and difference orbitals. The calculated energies are compared with existing and new experimental data obtained from Auger spectra, double charge transfer, and photoionization including the PIPICO technique. A complete assignment of the manifolds of singlet states is achieved with good agreement between theory and experiment. Only the lowest doubly charged ion states are well described by simple two-hole configurations, while three-hole one-particle configurations are important at higher energy. It is confirmed that the triplet ground states of these ions are well populated by photoionization, while the excited singlet states are revealed most clearly by the double charge transfer technique.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450518
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  • 7
    Electronic Resource
    Electronic Resource
    Photodissociation processes of water vapor below and above the ionization potential (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 584-596 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence excitation spectra of OH(A), OH(B), OH(C), Lyman α, Balmer α, Balmer β, and H2O+(A˜) are recorded in H2O in the 9–35 eV photon excitation range. The OH(A) fluorescence quantum yield is measured from 9.2 to 13.6 eV incident photon energy. The pressure dependence of the H2O+(A˜) fluorescence excitation spectrum is investigated and the quenching rate constant of H2O+(A˜) by H2O is found to be equal to (4±2)×10−10 cm3 s−1. New Rydberg states are observed: a continuum-like state in the 10–12.6 eV range assigned to the (3a1)−1 (3pb2) 1B2 state and two broad bands lying at 27–29 and 30–32 eV, respectively, assigned to Rydberg states converging towards the (2a1)−1 innervalence state of H2O+. The valence character of the nsa1 Rydberg states is discussed. The decay processes of valence-type vs pure Rydberg states are investigated. All energetically accessible dissociation channels producing fluorescent fragments are observed and the fragments appear at their thermodynamical threshold. The competition between autoionization and dissociation into neutrals is shown to occur only for pure Rydberg states. Possible dissociation mechanisms are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449525
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  • 8
    Electronic Resource
    Electronic Resource
    Fragmentation of the hexafluorobenzene dication formed by photoabsorption in the 30–120 eV energy range (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 1931-1941 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation pattern of the doubly charged C6F2+6 ion produced by single photon ionization has been investigated in the 27–120 eV energy range using time-of-flight (TOF) mass spectrometry, double photoion–photoion coincidence (PIPICO), and triple photoelectron–photoion–photoion coincidence (PEPIPICO) spectroscopies. A "metastable'' C6F2+6 ion is observed with an appearance energy of 27.3±0.4 eV dissociating slowly to the lowest thermodynamical limit leading to the ion pair products CF++C5F+5 (appearance energy of 30.7±0.5 eV). At higher energies, several other charge separation reactions appear as well as covalent channels in which neutral fragments are ejected from C6F2+6. Additional pairs of correlated ions are formed by secondary fragmentations. In the threshold region, double ionization of the molecule is probably followed by structural rearrangements to distinct C6F2+6 isomers, each dissociating to specific dissociation channels. Partial cross sections of selected ion pairs measured in the 30–120 eV photon energy region exhibit strong resonances suggesting that a rather large part of double ionization is an indirect phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462094
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  • 9
    Electronic Resource
    Electronic Resource
    Relaxation processes following excitation and ionization of SiF4 in the vicinity of the silicon 2p threshold. I. Electronic relaxation processes (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7071-7077 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoelectron and Auger spectra of SiF4 have been measured, using synchrotron radiation in the 100 to 125 eV photon energy range in the vicinity of the Si2p ionization threshold. Partial photoionization cross sections have been obtained for outer, inner valence states and satellite states in the same energy range, together with the threshold photoelectron spectrum. At the energies of the discrete resonances observed below 112 eV, the core excited molecule is found to decay mostly by resonant Auger and to a small extent by autoionization. Among the resonant Auger pathways, those in which two electrons (rather than one) are ejected are found to play a dominant role. Above threshold, especially around the energy of the first continuum resonance, normal Auger processes are observed. Also, we offer a new interpretation of the Auger spectrum based on large configuration interaction in the final state and on the screening of the Si2p hole by the lone-pair electrons of the fluorine atoms. We also find some evidence of cascade Auger processes which explain the formation of triply ionized molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456235
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  • 10
    Electronic Resource
    Electronic Resource
    Relaxation processes following excitation and ionization of SiF4 in the vicinity of the silicon 2p threshold. II. Dissociation of the molecular ions (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7078-7086 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Partial ion yields from photoionization of SiF4 have been measured with time-of-flight mass spectrometry, photoion–photoion coincidence and triple photoion coincidence techniques using synchrotron radiation from 100 to 136 eV, in the region of the silicon 2p edge where strong resonances are found. From the photon energy dependence of positive ion pairs and of doubly charged fragment intensities, with a suitable normalization procedure, we have estimated the total double photoionization cross section. Below the Si2p edge, the double to single dissociative ionization branching ratio follows the resonance behavior, and is consistent with the photoelectron results of de Souza et al. (Paper I) and discussed in terms of multibond breaking dissociation pathways of residual excited ions (singly and doubly charged) produced by resonant Auger decay processes. Above the Si2p edge, the fragmentation is found to originate from dissociative double ionization occurring after normal Auger processes. The small additional contribution of triple dissociative ionization is consistent with a second order Auger process. In contrast, the underlying valence ionization continuum is responsible for all parent intensity and most of the SiF+3 fragment expected from the normal dissociative ionization channels. The measurement of appearance energies of fragment ion pairs by the photoion–photoion coincidence method, offers a direct measurement of the first direct double ionization onset in SiF4 and new values for other dissociative SiF2+4 states which complement those found by Auger spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456236
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