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Full-Text Articles in Physics

Analytical Modeling And Numerical Simulations Of Time Delays In Attosecond Streaking Of One- And Two-Photon Ionization, Cory Scott Goldsmith Jan 2018

Analytical Modeling And Numerical Simulations Of Time Delays In Attosecond Streaking Of One- And Two-Photon Ionization, Cory Scott Goldsmith

Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018)

The generation of attosecond-duration (1 as = 10-18 s) coherent light through the process of high-order harmonic generation has opened the perspective for probing fundamental processes, such as photoionization, on the natural timescale of electron dynamics in matter. One probing technique is the attosecond streaking method, in which the momentum of the photoelectron is measured as a function of the time delay between the ionizing, attosecond extreme ultraviolet (XUV) pulse, and a weak, femtosecond near-infrared (NIR) pulse which streaks the momentum of the photoelectron, known as a streaking trace. The observed trace contains time information about the photoionization process in ...


K-Shell X-Ray Spectroscopy Of Atomic Nitrogen, M. M. Sant'anna, Gunnar Ohrwall, Wayne C. Stolte, Alfred S. Schlachter, Dennis W. Lindle, B. M. Mclaughlin Mar 2012

K-Shell X-Ray Spectroscopy Of Atomic Nitrogen, M. M. Sant'anna, Gunnar Ohrwall, Wayne C. Stolte, Alfred S. Schlachter, Dennis W. Lindle, B. M. Mclaughlin

Chemistry and Biochemistry Faculty Publications

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64 ± 0.02 eV was determined for the K-shell binding energy.


Low-Energy Nondipole Effects In Molecular Nitrogen Valence-Shell Photoionization, Oliver Hemmers, Renaud Guillemin, D. Rolles, A. Wolska, Dennis W. Lindle, E. P. Kanter, B. Krassig, S. H. Southworth, R. Wehlitz, B. Zimmermann, V. Mckoy, P. W. Langhoff Sep 2006

Low-Energy Nondipole Effects In Molecular Nitrogen Valence-Shell Photoionization, Oliver Hemmers, Renaud Guillemin, D. Rolles, A. Wolska, Dennis W. Lindle, E. P. Kanter, B. Krassig, S. H. Southworth, R. Wehlitz, B. Zimmermann, V. Mckoy, P. W. Langhoff

Environmental Studies Faculty Publications

Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3σg, 1πu, and 2σu shells of N2 exhibit spectral variations with incident photon energies from thresholds to ∼200  eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)⊗(M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization ...


Nondipole Effects In The Photoionization Of Xe 4d5/2 And 4d3/2: Evidence For Quadrupole Satellites, Oliver Hemmers, Renaud Guillemin, D. Rolles, A. Wolska, Dennis W. Lindle, K. T. Cheng, W. R. Johnson, H. L. Zhou, S. T. Manson Sep 2004

Nondipole Effects In The Photoionization Of Xe 4d5/2 And 4d3/2: Evidence For Quadrupole Satellites, Oliver Hemmers, Renaud Guillemin, D. Rolles, A. Wolska, Dennis W. Lindle, K. T. Cheng, W. R. Johnson, H. L. Zhou, S. T. Manson

Environmental Studies Faculty Publications

Measurements of nondipole parameters in spin-orbit-resolved Xe 4d photoionization demonstrate dynamical differences arising from relativistic effects. The experimental data do not agree with relativistic random-phase approximation calculations of single ionization dipole and quadrupole channels. It is suggested that the discrepancy is due to the omission of multiple-excitation quadrupole channels, i.e., quadrupole satellite transitions.


Nearest-Neighbor-Atom Core-Hole Transfer In Isolated Molecules, Renaud Guillemin, Oliver Hemmers, D. Rolles, S. W. Yu, A. Wolska, I. Tran, A. C. Hudson, J. Baker, Dennis W. Lindle Jun 2004

Nearest-Neighbor-Atom Core-Hole Transfer In Isolated Molecules, Renaud Guillemin, Oliver Hemmers, D. Rolles, S. W. Yu, A. Wolska, I. Tran, A. C. Hudson, J. Baker, Dennis W. Lindle

Environmental Studies Faculty Publications

A new phenomenon sensitive only to next-door-neighbor atoms in isolated molecules is demonstrated using angle-resolved photoemission of site-selective core electrons. Evidence for this interatomic core-to-core electron interaction is observable only by measuring nondipolar angular distributions of photoelectrons. In essence, the phenomenon acts as a very fine atomic-scale sensor of nearest-neighbor elemental identity.


Dramatic Nondipole Effects In Low-Energy Photoionization: Experimental And Theoretical Study Of Xe 5s, Oliver Hemmers, Renaud Guillemin, E. P. Kanter, B. Krassig, Dennis W. Lindle, S. H. Southworth, R. Wehlitz, J. Baker, A. C. Hudson, M. Lotrakul, D. Rolles, Wayne C. Stolte, I. Tran, A. Wolska, S. Yu, M. Ya Amusia, K. T. Cheng, L. V. Chernysheva, W. R. Johnson, S. T. Manson Aug 2003

Dramatic Nondipole Effects In Low-Energy Photoionization: Experimental And Theoretical Study Of Xe 5s, Oliver Hemmers, Renaud Guillemin, E. P. Kanter, B. Krassig, Dennis W. Lindle, S. H. Southworth, R. Wehlitz, J. Baker, A. C. Hudson, M. Lotrakul, D. Rolles, Wayne C. Stolte, I. Tran, A. Wolska, S. Yu, M. Ya Amusia, K. T. Cheng, L. V. Chernysheva, W. R. Johnson, S. T. Manson

Environmental Studies Faculty Publications

The Xe 5s nondipole photoelectron parameter γ is obtained experimentally and theoretically from threshold to ∼200  eV photon energy. Significant nondipole effects are seen even in the threshold region of this valence shell photoionization. In addition, contrary to previous understanding, clear evidence of interchannel coupling among quadrupole photoionization channels is found.


E1-E2 Interference In The Vuv Photoionization Of He, E. P. Kanter, B. Krassig, S. H. Southworth, Renaud Guillemin, Oliver Hemmers, Dennis W. Lindle, R. Wehlitz, M. Ya Amusia, L. V. Chernysheva, N. L. S. Martin Jul 2003

E1-E2 Interference In The Vuv Photoionization Of He, E. P. Kanter, B. Krassig, S. H. Southworth, Renaud Guillemin, Oliver Hemmers, Dennis W. Lindle, R. Wehlitz, M. Ya Amusia, L. V. Chernysheva, N. L. S. Martin

Environmental Studies Faculty Publications

We have measured the forward-backward asymmetry of photoelectron angular distributions produced in the vacuum ultraviolet photoionization of helium. This asymmetry, a consequence of the breakdown of the dipole approximation, measures the real part of the ratio of the quadrupole and dipole matrix elements. In the autoionization region, the strong energy dependence of the asymmetry permits an experimental separation of the ratio of those magnitudes from their phase difference. We experimentally determined the Fano parameters of the 2p21D2 quadrupole resonance, and report improved values of the width Γ and line profile parameter q from those previously available ...


Photoexcitation Of A Dipole-Forbidden Resonance In Helium, B. Krassig, E. P. Kanter, S. H. Southworth, Renaud Guillemin, Oliver Hemmers, Dennis W. Lindle, R. Wehlitz, N. L. S. Martin May 2002

Photoexcitation Of A Dipole-Forbidden Resonance In Helium, B. Krassig, E. P. Kanter, S. H. Southworth, Renaud Guillemin, Oliver Hemmers, Dennis W. Lindle, R. Wehlitz, N. L. S. Martin

Environmental Studies Faculty Publications

We have observed photoexcitation of the dipole-forbidden 1s21S0→2p21D2 resonance in helium by measuring the nondipolar forward-backward asymmetry of photoelectron angular distributions in the 2ℓ2ℓ autoionizing region. By exploiting the electric dipole-quadrupole interference in the excitation of both the 2s2p1P1 and 2p21D2 levels, we have observed the quadrupole resonance in photoabsorption and extracted its Fano line shape parameters and the relative phase of the 1sEp and 1sEd continua. We find the quadrupole line profile index q2 to be markedly different from theoretical expectations.


Large Nondipole Effects In The Angular Distributions Of K-Shell Photoelectrons From Molecular Nitrogen, Oliver Hemmers, H. Wang, P. Focke, I. A. Sellin, Dennis W. Lindle, J. C. Arce, J. A. Sheehy, P. W. Langhoff Dec 2001

Large Nondipole Effects In The Angular Distributions Of K-Shell Photoelectrons From Molecular Nitrogen, Oliver Hemmers, H. Wang, P. Focke, I. A. Sellin, Dennis W. Lindle, J. C. Arce, J. A. Sheehy, P. W. Langhoff

Environmental Studies Faculty Publications

Measurements of angular distributions of K-shell electrons photoejected from molecular nitrogen are reported which reveal large deviations at relatively low photon energies ( ħω≤500eV) from emission patterns anticipated from the dipole approximation to interactions between radiation and matter. A concomitant theoretical analysis incorporating the effects of electromagnetic retardation attributes the observed large nondipole behaviors in N2 to bond-length-dependent terms in the E1⊗(E2,M1) photoelectron emission amplitudes which are indicative of a potentially universal nondipole behavior in molecular photoionization.


Dynamical Relativistic Effects In Photoionization: Spin-Orbit-Resolved Angular Distributions Of Xenon 4d Photoelectrons Near The Cooper Minimum, H. Wang, G. Snell, Oliver Hemmers, M. M. Sant'anna, I. A. Sellin, N. Berrah, Dennis W. Lindle, P. C. Deshmukh, N. Haque, S. T. Manson Sep 2001

Dynamical Relativistic Effects In Photoionization: Spin-Orbit-Resolved Angular Distributions Of Xenon 4d Photoelectrons Near The Cooper Minimum, H. Wang, G. Snell, Oliver Hemmers, M. M. Sant'anna, I. A. Sellin, N. Berrah, Dennis W. Lindle, P. C. Deshmukh, N. Haque, S. T. Manson

Environmental Studies Faculty Publications

Two decades ago, it was predicted [Y. S. Kim et al., Phys. Rev. Lett. 46, 1326 (1981)] that relativistic effects should alter the dynamics of the photoionization process in the vicinity of Cooper minima. The present experimental and theoretical study of the angular distributions of Xe 4d3/2 and 4d5/2 photoelectrons demonstrates this effect for the first time. The results clearly imply that relativistic effects are likely to be important for intermediate- Z atoms at most energies.


Relativistic Effects On Interchannel Coupling In Atomic Photoionization: The Photoelectron Angular Distribution Of Xe, Oliver Hemmers, S. T. Manson, M. M. Sant'anna, P. Focke, H. Wang, I. A. Sellin, Dennis W. Lindle Jul 2001

Relativistic Effects On Interchannel Coupling In Atomic Photoionization: The Photoelectron Angular Distribution Of Xe, Oliver Hemmers, S. T. Manson, M. M. Sant'anna, P. Focke, H. Wang, I. A. Sellin, Dennis W. Lindle

Environmental Studies Faculty Publications

Measurements of the photoelectron angular-distribution asymmetry parameter β for Xe 5s photoionization have been performed in the 80–200 eV photon-energy region. The results show a substantial deviation from the nonrelativistic value of β=2 and provide a clear signature of significant relativistic effects in interchannel coupling.


Anionic Photofragmentation Of Co: A Selective Probe Of Core-Level Resonances, Wayne C. Stolte, D. L. Hansen, Maria Novella Piancastelli, I. Dominguez-Lopez, A. Rizvi, Oliver Hemmers, H. Wang, Alfred S. Schlachter, M. S. Lubell, Dennis W. Lindle May 2001

Anionic Photofragmentation Of Co: A Selective Probe Of Core-Level Resonances, Wayne C. Stolte, D. L. Hansen, Maria Novella Piancastelli, I. Dominguez-Lopez, A. Rizvi, Oliver Hemmers, H. Wang, Alfred S. Schlachter, M. S. Lubell, Dennis W. Lindle

Environmental Studies Faculty Publications

Anion-yield spectroscopy using x rays is shown to be a selective probe of molecular core-level processes, providing unique experimental verification of shape resonances. For CO, partial anion and cation yields are presented for photon energies near the C K edge. The O- yield exhibits features above threshold related only to doubly excited states, in contrast to cation yields which also exhibit pronounced structure due to the well-known σ* shape resonance. Because the shape resonance is completely suppressed for O-, anion spectroscopy thus constitutes a highly selective probe, yielding information unobtainable with absorption or electron spectroscopy.


Interchannel Coupling In The Photoionization Of The M-Shell Of Kr Well Above Threshold: Experiment And Theory, H. S. Chakraborty, D. L. Hansen, Oliver Hemmers, P. C. Deshmukh, P. Focke, I. A. Sellin, Clemens Heske, Dennis W. Lindle, S. T. Manson Apr 2001

Interchannel Coupling In The Photoionization Of The M-Shell Of Kr Well Above Threshold: Experiment And Theory, H. S. Chakraborty, D. L. Hansen, Oliver Hemmers, P. C. Deshmukh, P. Focke, I. A. Sellin, Clemens Heske, Dennis W. Lindle, S. T. Manson

Environmental Studies Faculty Publications

Photoionization cross sections and asymmetry (β) parameters for Kr 3s, 3p, and 3d subshells have been measured and calculated in the 300–1300-eV photon energy range. Good agreement between experiment and theory is found for both cross-section branching ratios and β parameters. Interchannel coupling among the channels arising from 3s, 3p, and 3d subshells is found to be necessary for quantitative accuracy of the theory. This shows that the interchannel coupling phenomenology far above threshold, found previously for outer shells of Ne and Ar, is also operative for inner atomic shells.


Photoelectron Spectroscopy And The Dipole Approximation, Oliver Hemmers, Dennis W. Lindle Jan 2001

Photoelectron Spectroscopy And The Dipole Approximation, Oliver Hemmers, Dennis W. Lindle

Environmental Studies Faculty Publications

Over the past three decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Advances in gas-phase photoemission experiments using synchrotron radiation have recently highlighted nondipole effects at relatively low photon energies while probing the limits of the dipole approximation. Breakdowns in this approximation are manifested primarily as deviations from dipolar angular distributions of photoelectrons. Detailed new results demonstrate nondipolar angular-distribution effects are easily observable in atomic gases at energies well below 1 keV, and, in molecules, a previously unexpected phenomenon greatly enhances the breakdown of the dipole approximation just above the core-level ...


Beyond The Dipole Approximation: Angular-Distribution Effects In The 1s Photoemission From Small Molecules, Dennis W. Lindle, Oliver Hemmers, H. Wang, P. Focke, I. A. Sellin, J. D. Mills, J. A. Sheehy, P. W. Langhoff Jan 2000

Beyond The Dipole Approximation: Angular-Distribution Effects In The 1s Photoemission From Small Molecules, Dennis W. Lindle, Oliver Hemmers, H. Wang, P. Focke, I. A. Sellin, J. D. Mills, J. A. Sheehy, P. W. Langhoff

Environmental Studies Faculty Publications

Over the past two decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Recent experiments on the 1s inner shells of small molecules at relatively low photon energies (⩽ 1000 eV) show strong nondipole effects. They are significant and measurable at energies close to threshold, in conflict with a common assumption that the dipole approximation is valid for photon energies below 1 keV.


Validity Of The Independent-Particle Approximation In X-Ray Photoemission: The Exception, Not The Rule, D. Hansen, Oliver Hemmers, H. Wang, Dennis W. Lindle, P. Focke, I. A. Sellin, Clemens Heske, H. S. Chakraborty, P. C. Deshmukh, S. T. Manson Oct 1999

Validity Of The Independent-Particle Approximation In X-Ray Photoemission: The Exception, Not The Rule, D. Hansen, Oliver Hemmers, H. Wang, Dennis W. Lindle, P. Focke, I. A. Sellin, Clemens Heske, H. S. Chakraborty, P. C. Deshmukh, S. T. Manson

Environmental Studies Faculty Publications

A combined experimental and theoretical study of argon valence photoionization illustrates the discovery of the broad lack of validity of the independent-particle approximation (IPA) for x-ray photoemission. In addition to previously known breakdowns of the IPA, which are limited to high photon energies and regions very near threshold, the observed breakdown in photoionization at intermediate energies demonstrates generally that the IPA is valid only in very restricted domains. These restrictions are expected to be relevant throughout the periodic table, with consequences for a wide variety of applications.


Photofragmentation Of Third-Row Hydrides Following Photoexcitation At Deep-Core Levels, D. Hansen, M. E. Arrasate, J. Cotter, G. R. Fisher, Oliver Hemmers, K. T. Leung, Jon C. Levin, R. Martin, Paul Neill, Rupert C. Perera, I. A. Sellin, Marc Simon, Y. Uehara, B. Vanderford, S. B. Whitfield, Dennis W. Lindle Nov 1998

Photofragmentation Of Third-Row Hydrides Following Photoexcitation At Deep-Core Levels, D. Hansen, M. E. Arrasate, J. Cotter, G. R. Fisher, Oliver Hemmers, K. T. Leung, Jon C. Levin, R. Martin, Paul Neill, Rupert C. Perera, I. A. Sellin, Marc Simon, Y. Uehara, B. Vanderford, S. B. Whitfield, Dennis W. Lindle

Environmental Studies Faculty Publications

The relaxation dynamics of HCl, DCl, H2S, and D2S following photoexcitation in the vicinities of the Cl and S K-shell thresholds (∼2.8keV for Cl, ∼2.5 keV for S) were studied by means of ion time-of-flight mass spectroscopy. In all cases, the onset of pre-edge core-shell photoionization precedes the formation on resonance of a significant amount of neutral hydrogen as well as postcollision-interaction effects above threshold. Examination of the width of the H+ peak in spectra taken with the analyzer parallel and perpendicular to the polarization vector of the incident light indicates that on resonance ...


Neutral Dissociation Of Hydrogen Following Photoexcitation Of Hcl At The Chlorine K Edge, D. L. Hansen, J. Cotter, G. R. Fisher, K. T. Leung, R. Martin, Paul Neill, Rupert C. Perera, I. A. Sellin, Marc Simon, Y. Uehara, B. Vanderford, S. B. Whitfield Apr 1998

Neutral Dissociation Of Hydrogen Following Photoexcitation Of Hcl At The Chlorine K Edge, D. L. Hansen, J. Cotter, G. R. Fisher, K. T. Leung, R. Martin, Paul Neill, Rupert C. Perera, I. A. Sellin, Marc Simon, Y. Uehara, B. Vanderford, S. B. Whitfield

Chemistry and Biochemistry Faculty Publications

Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge (~2.8 keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6ơ* antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cln1 ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs). [S1050-2947(98)03604-X]


Breakdown Of The Independent Particle Approximation In High-Energy Photoionization, E. W. B. Dias, H. S. Chakraborty, P. C. Deshmukh, S. T. Manson, Oliver Hemmers, P. Glans, D. Hansen, H. Wang, S. B. Whitfield, Dennis W. Lindle, R. Wehlitz, Jon C. Levin, I. A. Sellin Jun 1997

Breakdown Of The Independent Particle Approximation In High-Energy Photoionization, E. W. B. Dias, H. S. Chakraborty, P. C. Deshmukh, S. T. Manson, Oliver Hemmers, P. Glans, D. Hansen, H. Wang, S. B. Whitfield, Dennis W. Lindle, R. Wehlitz, Jon C. Levin, I. A. Sellin

Environmental Studies Faculty Publications

The independent particle approximation is shown to break down for the photoionization of both inner and outer nℓ (ℓ>0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed.


Observation Of Parity-Unfavored Transitions In The Nonresonant Photoionization Of Argon, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, R. Wehlitz, U. Becker Feb 1995

Observation Of Parity-Unfavored Transitions In The Nonresonant Photoionization Of Argon, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, R. Wehlitz, U. Becker

Environmental Studies Faculty Publications

Single-photon ionization of an atom or molecule can be subdivided into parity-favored and -unfavored transitions, the latter characterized by electron emission, preferentially perpendicular to the electric vector. The nonresonant existence of these transitions is shown experimentally and studied over an extended energy range for a variety of satellite transitions in atomic argon. The spectra exhibit several clearly resolved satellite lines with strongly negative β values close to -1, independent of the photon energy. The results confirm the corresponding predictions of angular-momentum transfer theory.


Observation Of Non-Isotropic Auger Angular Distribution In The C(1s) Shape Resonance Of Co, Oliver Hemmers, Franz Heiser, J. Eiben, R. Wehlitz, U. Becker Aug 1993

Observation Of Non-Isotropic Auger Angular Distribution In The C(1s) Shape Resonance Of Co, Oliver Hemmers, Franz Heiser, J. Eiben, R. Wehlitz, U. Becker

Environmental Studies Faculty Publications

Angle-resolved high-resolution C(KVV) Auger spectra of CO were taken in the vicinity of the C(1s) σ* shape resonance. These spectra show clear evidence for the theoretically predicted anisotropic K-shell Auger emission in molecules. Complementary results from angle-resolved photoion spectroscopy show that the small size of the observed effect is, besides the varying intrinsic anisotropy of the Auger decay, also due to a smaller anisotropy in the primary absorption process than originally predicted but in good agreement with more recent calculations. Contrary to this, satellite Auger transitions show unexpectedly large anisotropies.


Multiplet-Changing Auger Transitions In Valence Double Photoionization, U. Becker, Oliver Hemmers, B. Langer, I. Lee, A. Menzel, R. Wehlitz, M. Ya Amusia Feb 1993

Multiplet-Changing Auger Transitions In Valence Double Photoionization, U. Becker, Oliver Hemmers, B. Langer, I. Lee, A. Menzel, R. Wehlitz, M. Ya Amusia

Environmental Studies Faculty Publications

The decay of valence satellite states in neon above the first double-ionization threshold has been studied experimentally and theoretically. Special emphasis was given to differentiate between two decay modes: valence Auger and valence-multiplet Auger decay. It is shown that the latter process is predominant in the low kinetic energy part of the spectrum. The main structures of this low-energy Auger spectrum could be designated by help of calculated transition energies and decay rates.


Evidence For Atomic Processes In Molecular Valence Double Ionization, U. Becker, Oliver Hemmers, B. Langer, A. Menzel, R. Wehlitz, W. B. Peatman Feb 1992

Evidence For Atomic Processes In Molecular Valence Double Ionization, U. Becker, Oliver Hemmers, B. Langer, A. Menzel, R. Wehlitz, W. B. Peatman

Environmental Studies Faculty Publications

Complete molecular valence-electron spectra were measured for CO. Unexpectedly, discrete lines at low kinetic energies were found, superimposed on a continuous energy spectrum representing direct double-ionization processes. The appearance of these lines is discussed in the context of the formation of the C++O+ ion pair near its associated threshold at 38.4 eV. It is ascribed to valence-excited repulsive (CO+)* states, which dissociate to a large part rapidly into atomic fragments before electronic relaxation takes place. From our spectra, partial cross sections for the different processes leading to dissociative valence double ionization are derived.


Electron-Energy And –Angular Distributions In The Double Photoionization Of Helium, R. Wehlitz, Franz Heiser, Oliver Hemmers, B. Langer, A. Menzel, U. Becker Dec 1991

Electron-Energy And –Angular Distributions In The Double Photoionization Of Helium, R. Wehlitz, Franz Heiser, Oliver Hemmers, B. Langer, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Photoelectron spectra of helium have been measured at different angles and at various energies above the double-ionization threshold up to 120 eV to investigate the behavior of the energy and angular distributions, of shake-off electrons. Both energy and angular distributions clearly show a U-shaped profile which turns to a flat curve near threshold pointing to a uniform intensity distribution over the kinetic energy for all angles in this excitation energy regime. Our results for the angular-distribution asymmetry parameter indicate qualitative agreement with theoretical predictions but fail to provide them quantitatively.


High-Resolution Photoelectron Spectrometry Study Of Conjugate Shakeup Processes In The Li 1s Threshold Region, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, U. Becker Feb 1991

High-Resolution Photoelectron Spectrometry Study Of Conjugate Shakeup Processes In The Li 1s Threshold Region, B. Langer, J. Viefhaus, Oliver Hemmers, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Partial cross sections and angular-distribution asymmetry parameters of diagram and satellite lines associated with Li 1s photoionization were measured using synchrotron-radiation excitation. Special emphasis was given to a high-resolution study of the 1P and 3P conjugate shakeup satellite lines testing qualitative predictions of the conjugate shakeup model: increasing σ and decreasing β values towards threshold, both being verified. Comparison with recent relaxed Hartree-Fock calculations shows good agreement for the 1P satellite, but demonstrates also that the present theory does not seem to be able to describe the cross-section behavior of the 3P satellite correctly.


Argon-Photoion–Auger-Electron Coincidence Measurements Following K-Shell Excitation By Synchrotron Radiation, Jon C. Levin, C. Biedermann, N. Keller, L. Liljeby, C.-S. O, R. T. Short, Ivan A. Sellin, Dennis W. Lindle Aug 1990

Argon-Photoion–Auger-Electron Coincidence Measurements Following K-Shell Excitation By Synchrotron Radiation, Jon C. Levin, C. Biedermann, N. Keller, L. Liljeby, C.-S. O, R. T. Short, Ivan A. Sellin, Dennis W. Lindle

Chemistry and Biochemistry Faculty Publications

Argon photoion spectra have been obtained for the first time in coincidence with K-LL and K-LM Auger electrons, as a function of photon energy. The simplified charge distributions which result exhibit a much more pronounced photon-energy dependence than do the more complicated noncoincident spectra. In the near-K-threshold region, Rydberg shakeoff of np levels, populated by resonant excitation of K electrons, occurs with significant probability, as do double-Auger processes and recapture of the K photoelectron through postcollision interaction.