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  • 1
    Electronic Resource
    Electronic Resource
    Shape resonance effects in the rotationally resolved photoelectron spectra of O2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5345-5346 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of theoretical and experimental studies of the rotationally resolved photoelectron spectra of O2 at low temperature leading to the v+=0, 1, and 2 levels of the X 2Πg state of O+2. A delayed, pulsed field ionization technique is used in conjunction with a coherent VUV radiation source to obtain high resolution spectra near threshold. The data are compared with theoretical results obtained using static-exchange photoelectron orbitals and a full description of the mixed Hund's case (a)–(b) ionic ground state. Agreement with experiment is good, especially for the v+=1 and v+=2 levels. Analysis of the rotational branch intensities yields detailed information on the angular momentum composition of the shape resonance near threshold. We also show that the dependence of the electronic transition moment on internuclear distance caused by the shape resonance leads to a significant dependence of the rotational branch intensity on ion vibrational level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459654
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  • 2
    Electronic Resource
    Electronic Resource
    Studies of valence shell photoionization of Cl2 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4887-4892 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report photoionization cross sections and photoelectron angular distributions for the 5σg, 2πu and 2πg orbitals of Cl2 from threshold to ∼20 eV photoelectron energy obtained using Hartree–Fock photoelectron orbitals. These studies were motivated by recent (2+1) resonance enhanced multiphoton ionization (REMPI) experiments via the 2 1Πg(2π3g4sσg) state which show strong non-Franck–Condon effects in the ion vibrational distribution suggesting that shape and/or autoionizing resonances may play a role near threshold. Previous single-photon experiments on the valence orbitals of Cl2 do not give a consistent picture of these cross sections at low energies. Our results show that there is a shape resonance in the kπu continuum. However, preliminary studies show that these πu cross sections have almost no dependence on internuclear distance and could not be the cause of non-Franck–Condon effects observed in the REMPI experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457705
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  • 3
    Electronic Resource
    Electronic Resource
    Shape resonance behavior in 1πg photoionization of O2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2575-2579 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report calculations of vibrationally resolved cross sections and photoelectron angular distributions for photoionization of O2 leading to the X 2 Πg (ν+ =0–4) states of O+2 using Hartree–Fock continuum photoelectron orbitals. These studies were motivated by recent results which show that a σu shape resonance plays a dominant role in producing non-Franck–Condon vibrational distributions in resonant multiphoton ionization of O2 via the C 3Πg (1πg3sσg) Rydberg state. In the present study, we investigate how this shape resonance influences photoionization dynamics in single-photon ionization. Below 21 eV photon energy, we find significant non-Franck–Condon effects in the vibrational branching ratios as well as in the vibrationally resolved photoelectron angular distributions. Substantial autoionization hinders a direct comparison between theory and experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455954
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  • 4
    Electronic Resource
    Electronic Resource
    Vibrational branching ratios and shape resonant photoionization dynamics in N2O (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1535-1543 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational branching ratios and photoelectron asymmetry parameters for alternative vibrational modes in the photoionization of N2O(7σ−1) have been studied using accurate photoelectron continuum orbitals. Earlier dispersed ionic fluorescence measurements [E. D. Poliakoff, M. H. Ho, M. G. White, and G. E. Leroi, Chem. Phys. Lett. 130, 91 (1986)] revealed strong non-Franck–Condon vibrational ion distributions for both the symmetric and antisymmetric stretching modes at low photoelectron energies. Our results establish that these features arise from a σ shape resonance which, based on its dependence on internuclear geometry, must be associated with the molecular framework as a whole and not with either of its fragments, N–N or N–O. This behavior accounts for the more pronounced deviations of the vibrational branching ratios from Franck–Condon values observed in the symmetric than in the antisymmetric mode. The σ continuum also supports a second shape resonance at higher energy which does not influence the vibrational branching ratios but is quite evident in the photoelectron asymmetry parameters around a photon energy of 40 eV. These vibrationally resolved studies of the photoelectron spectra of this polyatomic system provide an interesting example of the rich shape resonant behavior that can be expected to arise in polyatomic molecules with their alternative vibrational modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456096
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  • 5
    Electronic Resource
    Electronic Resource
    Multiplet-specific shape resonant features in vibrationally resolved 3σg photoionization of O2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 150-154 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report multiplet-specific vibrationally resolved photoionization cross sections and photoelectron angular distributions for the 3σg orbital of O2 leading to the v+=0–3 levels of the b 4Σ−g and B 2Σ−g states of O+2. These studies were motivated by recent work which shows significant nonstatistical behavior in the vibrationally unresolved spectrum at low photoelectron energies arising from the sensitivity of the kσu shape resonance to the multiplet-specific exchange potentials. In addition to the anticipated non-Franck–Condon vibrational distributions arising from the kσu shape resonance, we also find substantial nonstatistical effects in our vibrationally resolved cross sections and particularly in our photoelectron angular distributions over a broad energy range. Extensive electronic autoionization due to Rydberg levels leading to the c 4Σ−u (2σ−1u) ion makes it difficult to assess these effects in the available experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457493
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  • 6
    Electronic Resource
    Electronic Resource
    Shape resonances in the photoionization of N2O (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 224-228 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of studies of the cross sections and photoelectron asymmetry parameters for photoionization of the 7σ level of N2O using Hartree–Fock photoelectron continuum orbitals. These studies were motivated by recent measurements which showed significant non-Franck–Condon vibrational distributions at low photoelectron energies where previously only autoionizing resonances, but no shape resonance, had been identified. Our results establish that there are two σ shape resonances in the 7σ ionization continuum, a pronounced resonance at low photoelectron energies, and another at higher energy which is essentially obscured in the vibrationally unresolved cross sections. The shape resonant structure that emerges from these studies differs significantly from the predictions of previous model studies. Studies in progress reveal a rich and unusual dependence of these resonances on changes in internuclear distances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453620
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  • 7
    Electronic Resource
    Electronic Resource
    Multiplet-specific shape resonance and autoionization effects in (2+1) resonance enhanced multiphoton ionization of O2 via the d 1Πg state (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5319-5327 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we discuss the single-photon ionization dynamics of the d 1Πg Rydberg state of O2. Comparision is made with vibrationally resolved measurements of photoelectron spectra which employ (2+1) resonance enhanced multiphoton ionization (REMPI) through the d 1Πg state. A σu shape resonance near the ionization threshold leads to non-Franck–Condon vibrational branching ratios and a substantial dependence of photoelectron angular distributions on the vibrational state of the X 2Πg ion. Significant differences exist between our one-electron predictions and experiment. These are mainly attributed to electronic autoionization of repulsive 1∑−u, 1∑+u, and 1Δu states associated with the 1π3u1π3g configuration. A proposed singlet "K'' 1Πu Rydberg state converging to the A 2Πu ion probably also contributes to autoionization in the d 1Πg state spectrum. We also show that autoionizing H and J 3Πu Rydberg states of O2 converging to the a 4Πu and A 2Πu ionic thresholds, respectively, may play a previously unsuspected role in the C 3Πg state one-color REMPI spectra. We discuss multiplet-specific (spin-dependent) effects via comparision of these results with recent experimental and theoretical studies of O2C 3Πg photoionization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458511
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  • 8
    Electronic Resource
    Electronic Resource
    Cross sections and photoelectron asymmetry parameters for photoionization of H2O (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2362-2366 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The iterative Schwinger variational method is used to obtain cross sections and photoelectron asymmetry parameters for photoionization of the three outermost valence orbitals (1b1, 3a1, and 1b2) of H2O for photon energies from near threshold to 50 eV. A comparison of these calculated results with available experimental data is encouraging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457977
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  • 9
    Electronic Resource
    Electronic Resource
    Multiplet-specific shape resonant features in 3σg photoionization of O2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3931-3936 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report multiplet-specific photoionization cross sections and photoelectron angular distributions for the 3σg orbital of O2 leading to the b 4Σ−g and B 2Σ−g ion states obtained using Hartree–Fock photoelectron orbitals. These cross sections show significant nonstatistical behavior at low photoelectron energies which arises from the sensitivity of the kσu shape resonance to the exchange potentials of these two molecular ions. Specifically, the oscillator strength associated with the shape resonance in the B 2Σ−g cross section is shifted to lower energy compared to that of the b 4Σ−g cross section. This shift gives rise to a quartet to doublet cross section ratio of more than 15:1 near threshold. These effects are difficult to assess in the measured cross sections due to the presence of strong autoionization features. Significant multiplet dependence is also seen in the calculated photoelectron angular distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455803
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  • 10
    Electronic Resource
    Electronic Resource
    Shape resonance and non-Franck–Condon effects in (2+1) resonant enhanced multiphoton ionization of O2 via the C 3Πg state (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 633-640 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report vibrationally resolved photoelectron angular distributions for photoionization of the C 3Πg Rydberg state of O2. Comparison is made with recent experimental measurements of angular distributions which employ (2+1) resonant enhanced multiphoton ionization of the C 3Πg state. The present theory treats the process as single-photon ionization from an unaligned Rydberg state, and qualitatively accounts for much of the observed trends. Non-Franck–Condon effects induced by the kσu shape resonance lead to a substantial dependence of the angular distributions on the vibrational state of the X 2Πg ion. Discrepancies between our theoretical results and experiment are qualitatively discussed and tentatively attributed to residual electron correlations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456142
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