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Articles 91 - 120 of 123

Full-Text Articles in Biological and Chemical Physics

Near-Edge X-Ray Absorption Fine Structure Study Of Ion-Beam-Induced Phase Transformation In Gd2(Ti1-Yzry)2o7, Ponnusamy Nachimuthu, S. Thevuthasan, V. Shutthanandan, E. M. Adams, W. J. Weber, B. D. Begg, D. K. Shuh, Dennis W. Lindle, Eric M. Gullikson, Rupert C. Perera Jan 2005

Near-Edge X-Ray Absorption Fine Structure Study Of Ion-Beam-Induced Phase Transformation In Gd2(Ti1-Yzry)2o7, Ponnusamy Nachimuthu, S. Thevuthasan, V. Shutthanandan, E. M. Adams, W. J. Weber, B. D. Begg, D. K. Shuh, Dennis W. Lindle, Eric M. Gullikson, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

The structural and electronic properties of Gd2(Ti1−yZry)2O7 (y=0–1) pyrochlores following a 2.0-MeV Au2+ ion-beam irradiation (~5.0 X 1014 Au2+/cm2) have been investigated by Ti 2p and O 1s near-edge x-ray absorption fine structure (NEXAFS). The irradiation of Gd2(Ti1−yZry)2O7 leads to the phase transformation from the ordered pyrochlore structure (Fd3m) to the defect fluorite structure (Fm3m) regardless of Zr concentration. Irradiated Gd2(Ti1−y …

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Fragmentation Dynamics Of H2s Following S 2p Photoexcitation, Renaud Guillemin, S-W Yu, Wayne C. Stolte, Dennis W. Lindle Jan 2005

Fragmentation Dynamics Of H2s Following S 2p Photoexcitation, Renaud Guillemin, S-W Yu, Wayne C. Stolte, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

The fragmentation dynamics of core-excited H2S has been studied by means of partial anion and cation yield measurements around the S L2,3-subshell ionization thresholds. All detectable ionic fragments are reported, and significant differences between partial ion yields are observed. Possible dissociation pathways are discussed by comparison to previous studies of electron spectra.

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Anion And Cation-Yield Spectroscopy Of Core-Excited Sf6, Maria Novella Piancastelli, Wayne C. Stolte, Renaud Guillemin, A. Wolska, M. M. Sant'anna, Dennis W. Lindle Jan 2005

Anion And Cation-Yield Spectroscopy Of Core-Excited Sf6, Maria Novella Piancastelli, Wayne C. Stolte, Renaud Guillemin, A. Wolska, M. M. Sant'anna, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

We report an extensive study on total and partial-ion-yield spectroscopy around both the S 2p and F 1s thresholds in SF6. All positive and negative single-ion channels have been measured. Below the F 1s threshold we detect a large variation in relative intensity of the resonant structures according to the specific channel monitored, indicating selective fragmentation. Above threshold, at variance with previous cases described by us, we detect high-intensity structures related to shape resonances not only in the cation channels but also for the anions. We discuss the applicability and limits of a model we …

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Probing Cation Antisite Disorder In Gd2ti2o7 Pyrochlore By Site-Specific Nexafs And Xps, Ponnusamy Nachimuthu, S. Thevuthasan, Mark H. Engelhard, W. J. Weber, D. K. Shuh, N. M. Hamdan, B. S. Mun, E. M. Adams, D. E. Mccready, V. Shutthanandan, Dennis W. Lindle, G. Balakrishnan, R. C. Ewing Sep 2004

Probing Cation Antisite Disorder In Gd2ti2o7 Pyrochlore By Site-Specific Nexafs And Xps, Ponnusamy Nachimuthu, S. Thevuthasan, Mark H. Engelhard, W. J. Weber, D. K. Shuh, N. M. Hamdan, B. S. Mun, E. M. Adams, D. E. Mccready, V. Shutthanandan, Dennis W. Lindle, G. Balakrishnan, R. C. Ewing

Chemistry and Biochemistry Faculty Research

Disorder in Gd2Ti2O7 is investigated by near-edge x-ray-absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS). NEXAFS shows Ti4+ ions occupy octahedral sites with a tetragonal distortion induced by vacant oxygen sites. O 1s XPS spectra obtained with a charge neutralization system from Gd2Ti2O7(100) and the Gd2Ti2O7 pyrochlore used by Chen et al. [Phys. Rev. Lett. 88, 105901 (2002)], both yielded a single peak, unlike the previous result on the latter that found two peaks. The current results give no evidence for …

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Performance Characteristics Of Beamline 6.3.1 From 200 Ev To 2000 Ev At The Advanced Light Source, Ponnusamy Nachimuthu, J. H. Underwood, C. D. Kemp, Eric M. Gullikson, Dennis W. Lindle, David K. Shuh, Rupert C. Perera Jan 2004

Performance Characteristics Of Beamline 6.3.1 From 200 Ev To 2000 Ev At The Advanced Light Source, Ponnusamy Nachimuthu, J. H. Underwood, C. D. Kemp, Eric M. Gullikson, Dennis W. Lindle, David K. Shuh, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

Bend magnet beamline 6.3.1 at the Advanced Light Source operates from 200 eV to 2000 eV, primarily used for x-ray absorption fine structure investigations. The beamline optics consist of a compact, entrance-slitless, Hettrick-Underwood type variable-line-spacing plane-grating monochromator and refocusing mirrors to provide a 25 μm × 500 μm spot at the focal point in the reflectometer end station. Wavelength is scanned by the simple rotation of the grating and illuminates a fixed exit slit. The LabView based beamline control and data acquisition computer code has been implemented to provide a convenient interface to the user. The dedicated end station is …

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Photofragmentation Dynamics Of Core-Excited Water By Anion-Yield Spectroscopy, Wayne C. Stolte, M. M. Sant'anna, Gunnar Ohrwall, Maria Novella Piancastelli, I. Dominguez-Lopez, Dennis W. Lindle Aug 2003

Photofragmentation Dynamics Of Core-Excited Water By Anion-Yield Spectroscopy, Wayne C. Stolte, M. M. Sant'anna, Gunnar Ohrwall, Maria Novella Piancastelli, I. Dominguez-Lopez, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Partial-anion and- cation yields from H2O are presented for photon energies near the oxygen K edge. The O- yield exhibits a feature above threshold attributed to doubly excited states, in contrast to the H- and cation yields, which are nearly featureless above threshold. Additionally, the lack of the OH- fragment indicates radiative decay and provides a negligible amount of anion formation.

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Comparison Between The Ultraviolet Emission From Pulsed Microhollow Cathode Discharges In Xenon And Argon, Isfried Petzenhauser, Leopold D. Biborosch, Uwe Ernst, Klaus Frank, Karl H. Schoenbach Jan 2003

Comparison Between The Ultraviolet Emission From Pulsed Microhollow Cathode Discharges In Xenon And Argon, Isfried Petzenhauser, Leopold D. Biborosch, Uwe Ernst, Klaus Frank, Karl H. Schoenbach

Bioelectrics Publications

We measured the dynamic I–V characteristics and vacuum ultraviolet (VUV) emission lines of the second continuum in xenon (170 nm) and argon (130.5 nm) from pulsed microhollow cathode discharges (MHCD). For pulse lengths between 1 and 100 μs the dynamic I–V characteristics are similar in both inert gases. Only the time variation of the VUV emission line at 170 nm for xenon can be related to the dimer excited states. In argon the energy transfer between the Ar*2 dimers and the oxygen impurity atoms is responsible for a qualitatively different time behavior of the resonance line at 130.5 nm. …

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Fragmentation Processes Following Core Excitation In Acetylene And Ethylene By Partial Ion Yield Spectroscopy, Maria Novella Piancastelli, Wayne C. Stolte, Gunnar Ohrwall, S-W Yu, D. Bull, K. Lantz, Alfred S. Schlachter, Dennis W. Lindle Nov 2002

Fragmentation Processes Following Core Excitation In Acetylene And Ethylene By Partial Ion Yield Spectroscopy, Maria Novella Piancastelli, Wayne C. Stolte, Gunnar Ohrwall, S-W Yu, D. Bull, K. Lantz, Alfred S. Schlachter, Dennis W. Lindle

Chemistry and Biochemistry Faculty Research

Partial ion yield spectroscopy provides a very detailed picture of fragmentation processes following core excitation in isolated molecules. We exploit this potential in the analysis of decay processes following C1s→π and C1s→Rydberg excitations in ethylene and acetylene. We show that the relative intensity of spectral features related to the excitation to empty molecular orbitals or to Rydberg states is a function of the time variation of the fragmentation process. Namely, we see an intensity increase in the Rydberg states compared to the molecular orbitals as the fragmentation process becomes more extensive, a result attributable to the diffuse nature of the …

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Holographic Analysis Of Diffraction Structure Factors, S. Marchesini, N. Mannella, C. S. Fadley, M. A. Van Hove, J. J. Bucher, D. K. Shuh, L. Fabris, M. J. Press, M. W. West, Wayne C. Stolte, Z. Hussain Sep 2002

Holographic Analysis Of Diffraction Structure Factors, S. Marchesini, N. Mannella, C. S. Fadley, M. A. Van Hove, J. J. Bucher, D. K. Shuh, L. Fabris, M. J. Press, M. W. West, Wayne C. Stolte, Z. Hussain

Chemistry and Biochemistry Faculty Research

We combine the theory of inside-source/inside-detector x-ray fluorescence holography and Kossel lines/x ray standing waves in kinematic approximation to directly obtain the phases of the diffraction structure factors. The influence of Kossel lines and standing waves on holography is also discussed. We obtain partial phase determination from experimental data obtaining the sign of the real part of the structure factor for several reciprocal lattice vectors of a vanadium crystal.

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In-Situ X-Ray-Absorption Spectroscopy Study Of Hydrogen Absorption By Nickel-Magnesium Thin Films, B. Farangis, Ponnusamy Nachimuthu, T. J. Richardson, J. L. Slack, Rupert C. Perera, Eric M. Gullikson, Dennis W. Lindle, M. Rubin Jul 2002

In-Situ X-Ray-Absorption Spectroscopy Study Of Hydrogen Absorption By Nickel-Magnesium Thin Films, B. Farangis, Ponnusamy Nachimuthu, T. J. Richardson, J. L. Slack, Rupert C. Perera, Eric M. Gullikson, Dennis W. Lindle, M. Rubin

Chemistry and Biochemistry Faculty Research

Structural and electronic properties of co-sputtered Ni-Mg thin films with varying Ni to Mg ratio were studied by in-situ x-ray absorption spectroscopy in the Ni L-edge and Mg K-edge regions. Co-deposition of the metals led to increased disorder and decreased coordination around Ni and Mg compared to pure metal films. Exposure of the metallic films to hydrogen resulted in formation of hydrides and increased disorder. The presence of hydrogen as a near neighbor around Mg caused a drastic reduction in the intensities of multiple scattering resonances at higher energies. The optical switching behavior and changes in the x-ray spectra varied …

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Shape Imprinting Due To Variable Disulfide Bonds In Polyacrylamide Gels, Andrew B. Greytak, Alexander Y. Grosberg, Toyoichi Tanaka Jun 2001

Shape Imprinting Due To Variable Disulfide Bonds In Polyacrylamide Gels, Andrew B. Greytak, Alexander Y. Grosberg, Toyoichi Tanaka

Faculty Publications

Through the use of variable disulfide crosslinkers, we have created polyacrylamide gels whose shape can be altered after polymerization. N,N'-bisacryloylcystamine is incorporated as a crosslinker, along with a smaller amount of a permanent crosslinker. After polymerization, the disulfide bonds are cleaved into thiols through reduction. By reoxidizing the thiols with the gel held in a new macroscopic shape, a new set of disulfide bonds is formed, and the gel is forced to adopt the new shape. Retension of the new shape improves with greater distortion from the original shape, as well as with increased concentration of variable …

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Reply To Comment On ‘Nondipole Resonant X-Ray-Raman Spectroscopy: Polarized Inelastic Scattering At The K Edge Of Cl2,’, J. D. Mills, J. A. Sheehy, T. A. Ferrett, S. H. Southworth, R. Mayer, Dennis W. Lindle, P. W. Langhoff Jan 1999

Reply To Comment On ‘Nondipole Resonant X-Ray-Raman Spectroscopy: Polarized Inelastic Scattering At The K Edge Of Cl2,’, J. D. Mills, J. A. Sheehy, T. A. Ferrett, S. H. Southworth, R. Mayer, Dennis W. Lindle, P. W. Langhoff

Chemistry and Biochemistry Faculty Research

Mills et al. Reply: In their Comment on our Letter [1], Gel’mukhanov and Ågren [2] reiterate recent assertions [3] based on their earlier theoretical studies [4]. The primary purpose of their Comment is apparently to refute our stated conclusion that core-excited-state localization/ delocalization mechanisms are irrelevant to interpretations of reported Raman scattering experiments on homonuclear diatomic molecules.

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Auger Resonance Decay Process In Ar 2p Shell Excitation And Ionization, Y. Lu, Wayne C. Stolte, J.A. R. Samson Oct 1998

Auger Resonance Decay Process In Ar 2p Shell Excitation And Ionization, Y. Lu, Wayne C. Stolte, J.A. R. Samson

Chemistry and Biochemistry Faculty Research

The production and subsequent autoionization of the Ar+ (1D2)6d1 satellite state that is formed either by shake-up or recapture during the Auger decay of a 2p vacancy in Ar has been studied by photoelectron spectroscopy in the energy region from 243 to 256 eV. The creation of near zero energy electrons below and immediately above the Ar 2p ionization threshold is discussed. Some ambiguous points in previous studies are clarified.

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Chemical Signals From Submarine Fluid Advection Onto The Continental Shelf, W. S. Moore, Timothy J. Shaw Sep 1998

Chemical Signals From Submarine Fluid Advection Onto The Continental Shelf, W. S. Moore, Timothy J. Shaw

Faculty Publications

No abstract provided.

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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 Research

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]

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Double Photoionization Of Helium, James A.R. Samson, Wayne C. Stolte, Z. X. He, Y. Lu, J. N. Cutler, R. J. Bartlett Mar 1998

Double Photoionization Of Helium, James A.R. Samson, Wayne C. Stolte, Z. X. He, Y. Lu, J. N. Cutler, R. J. Bartlett

Chemistry and Biochemistry Faculty Research

The cross sections for double photoionization of helium and the ratios of double to single ionization have been measured from the double-ionization threshold to 820 eV. The results are in very good agreement with several recent calculations.

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Ab Initio Study Of Formazan And 3-Nitroformazan, G. Buemi, F. Zuccarello, P. Venuvanalingam, M. Ramalingam, Salai Cheettu Ammal Jan 1998

Ab Initio Study Of Formazan And 3-Nitroformazan, G. Buemi, F. Zuccarello, P. Venuvanalingam, M. Ramalingam, Salai Cheettu Ammal

Faculty Publications

Formazan and 3-nitroformazan have been investigated at abinitio level (MP2/6-31G** and B3LYP/6-31G**) in all their possible conformations, for studying the various possibilities of intramolecular hydrogen bonding formation. The trans-syn-s-cis (TSSC), known also asyellowform, has been found to be the most stable conformer (at least in the gas phase) in both compounds. This particular structure is strongly stabilized by a N–H···N hydrogen bridge, which gives rise to a hexatomic chelate ring, with the possibility of a proton transfer process.This closely resembles that of malondialdehyde, previously studied, in the evolution of the …

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Ab Initio And Dft Investigations Of Lithium/Hydrogen Bonded Complexes Of Trimethylamine, Dimethyl Ether And Dimethyl Sulfide, Salai Cheettu Ammal, P. Venuvanalingam Jan 1998

Ab Initio And Dft Investigations Of Lithium/Hydrogen Bonded Complexes Of Trimethylamine, Dimethyl Ether And Dimethyl Sulfide, Salai Cheettu Ammal, P. Venuvanalingam

Faculty Publications

Ab initio and DFT computations have been carried out on LiF and HF complexes of a set of n-donors viz. trimethylamine, dimethyl ether and dimethyl sulfide with a 6-31++G(d,p) basis set. The effect of correlation has been included with MP2, MP4 and DFT calculations. NBO analyses of the wavefunctions have been performed to examine the intermolecular interaction at the orbital level. Calculations reveal that these donors form strong n→σ* complexes and computed binding energies of the (CH3)2O···HF complex agree very well with the experimental binding energies from IR spectroscopy. LiF forms stronger complexes than HF, …

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Nondipole Resonant X-Ray-Raman Spectroscopy: Polarized Inelastic Scattering At The K Edge Of Cl2, J. D. Mills, J. A. Sheehy, T. A. Ferrett, S. H. Southworth, R. Mayer, Dennis W. Lindle, P. W. Langhoff Jul 1997

Nondipole Resonant X-Ray-Raman Spectroscopy: Polarized Inelastic Scattering At The K Edge Of Cl2, J. D. Mills, J. A. Sheehy, T. A. Ferrett, S. H. Southworth, R. Mayer, Dennis W. Lindle, P. W. Langhoff

Chemistry and Biochemistry Faculty Research

Experimental and theoretical studies are reported on the inelastic (Raman) scattering of wavelength-selected polarized x rays from the K edge of gas-phase chlorine molecules. The polarized emission spectra exhibit prominent nondipole features consequent of phase variations of the incident and emitted radiation over molecular dimensions, as predicted by the Kramers-Heisenberg scattering formalism. Issues pursuant to the detection of core-hole localization by resonant Raman scattering from homonuclear diatomic molecules are critically examined. [S0031-9007(97)03486-8]

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Cross Sections For The Production Of He+ (Np) 2p0 States By 50 To 150 Kev Proton Impact On Helium, Wayne C. Stolte, R. Bruch Sep 1996

Cross Sections For The Production Of He+ (Np) 2p0 States By 50 To 150 Kev Proton Impact On Helium, Wayne C. Stolte, R. Bruch

Chemistry and Biochemistry Faculty Research

Cross sections have been measured for the production of He+ (np) 2Po states, n=2,3,4, by proton impact on helium over a projectile velocity range of 1.42–2.45 a.u. (50 ≤E≤150 keV). Cross sections were determined by measuring the extreme ultraviolet photons emitted from excited He1 ions. The data indicate a lower energy than expected for the maximum cross section. A comparison of the present results in terms of projectile energy dependance with the cross sections for excitation to He (1snp) 1Po, ionization, and total electron capture suggests the primary mechanism …

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Design And Performance Of The Advanced-Light-Source Double-Crystal Monochromator, G. Jones, S. Ryce, Dennis W. Lindle, B. A. Karlin, J. C. Woicik, Rupert C. Perera Feb 1995

Design And Performance Of The Advanced-Light-Source Double-Crystal Monochromator, G. Jones, S. Ryce, Dennis W. Lindle, B. A. Karlin, J. C. Woicik, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

A new “Cowan type” double-crystal monochromator, based on the boomerang design used at National Synchrotron Light Source (NSLS) beamline X-24A, has been developed for beamline 9.3.1 at the Advanced Light Source (ALS), a windowless ultrahigh vacuum beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design of the monochromator has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline …

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Three-Body Analytical Potential For Interacting Helium Atoms, Carol A. Parish, Clifford E. Dykstra Nov 1994

Three-Body Analytical Potential For Interacting Helium Atoms, Carol A. Parish, Clifford E. Dykstra

Chemistry Faculty Publications

Large basis set ab initio calculations have been carried out for a dense grid of points on the He, potential energy surface. Three-body contributions were extracted at every point, and a number of concise functional representations for the three-body potential surface were then examined. Three-body multipolar dispersion terms and other radial and angular terms were used in the representations, and an assessment of relative importance of the different terms is presented. Combined with a two-body He-He potential, the results of this work should offer a high quality interaction potential for simulations of aggregated helium.

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Pairwise And Many-Body Contributions To Interaction Potentials In He(N) Clusters, Carol A. Parish, Clifford E. Dykstra Jan 1993

Pairwise And Many-Body Contributions To Interaction Potentials In He(N) Clusters, Carol A. Parish, Clifford E. Dykstra

Chemistry Faculty Publications

High level ab initio calculations have been carried out to assess the pairwise additivity of potentials in the attractive or well regions of the potential surfaces of clusters of helium atoms. A large basis set was employed and calculations were done at the Brueckner orbital coupled cluster level. Differences between calculated potentials for several interacting atoms and the corresponding summed pair potentials reveal the three‐body and certain higher order contributions to the interaction strengths. Attraction between rare gas atoms develops from dispersion, and so helium clusters provide the most workable systems for analyzing nonadditivity of dispersion. The results indicate that …

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High-Energy Behavior Of The Double Photoionization Of Helium From 2 To 12 Kev, Jon C. Levin, Ivan A. Sellin, B. M. Johnson, Dennis W. Lindle, R. D. Miller, Y. Azuma, H. G. Berry, D.-H. Lee, N. Berrah Jan 1993

High-Energy Behavior Of The Double Photoionization Of Helium From 2 To 12 Kev, Jon C. Levin, Ivan A. Sellin, B. M. Johnson, Dennis W. Lindle, R. D. Miller, Y. Azuma, H. G. Berry, D.-H. Lee, N. Berrah

Chemistry and Biochemistry Faculty Research

We report the ratio of double-to-single photoionization of He at several photon energies from 2 to 12 keV. By time-of-Aight methods, we find a ratio consistent with an asymptote at 1.5%±0.2%, essentially reached by h v≈4 keV. Fair agreement is obtained with older shake calculations of Byron and Joachain [Phys. Rev. 164, 1 (1967)], of Aberg [Phys. Rev. A 2, 1726 (1970)], and with recent many-body perturbation theory (MBPT) of Ishihara, Hino, and McGuire [Phys. Rev. A 44, 6980 (1991)]. The result lies below earlier MPBT calculations by Amusia et al. [J. Phys. B 8 …

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Surface Structure Of √3x√3r 30 Cl/Ni(111) Determined Using Low-Temperature Angle-Resolved-Photoemission Extended Fine Structure, Li-Qiong Wang, Z. Hussain, Z. Q. Huang, A. E. Schach Von Wittenau, Dennis W. Lindle, D. A. Shirley Dec 1991

Surface Structure Of √3x√3r 30 Cl/Ni(111) Determined Using Low-Temperature Angle-Resolved-Photoemission Extended Fine Structure, Li-Qiong Wang, Z. Hussain, Z. Q. Huang, A. E. Schach Von Wittenau, Dennis W. Lindle, D. A. Shirley

Chemistry and Biochemistry Faculty Research

A surface structural study of the √3 × √3 R30° Cl/Ni(111) adsorbate system was made using low-temperature angle-resolved photoemission extended fine structure. The experiments were performed along two emission directions, [111] and [110], and at two temperatures, 120 and 300 K. The multiple-scattering spherical-wave analysis determined that the Cl atom adsorbs in the fcc threefold hollow site, 1.837(8) Å above the first nickel layer, with a Cl-Ni bond length of 2.332(6) Å, and an approximate 5% contraction between the first and the second nickel layers (the errors in parentheses are statistical standard deviations only).

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Measurement Of The Ratio Of Double-To-Single Photoionization Of Helium At 2.8 Kev Using Synchrotron Radiation, Jon C. Levin, Dennis W. Lindle, N. Keller, R. D. Miller, Y. Azuma, N. Berrah Mansour, H. G. Berry, Ivan A. Sellin Aug 1991

Measurement Of The Ratio Of Double-To-Single Photoionization Of Helium At 2.8 Kev Using Synchrotron Radiation, Jon C. Levin, Dennis W. Lindle, N. Keller, R. D. Miller, Y. Azuma, N. Berrah Mansour, H. G. Berry, Ivan A. Sellin

Chemistry and Biochemistry Faculty Research

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He++/He+=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%.

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Anisotropy Of Polarized X-Ray Emission From Molecules, S. H. Southworth, Dennis W. Lindle, R. Mayer, P. L. Cowan Aug 1991

Anisotropy Of Polarized X-Ray Emission From Molecules, S. H. Southworth, Dennis W. Lindle, R. Mayer, P. L. Cowan

Chemistry and Biochemistry Faculty Research

Strongly anisotropic, polarized Cl K-V x-ray emission from gas-phase CF3Cl has been observed following resonant excitation with a linearly polarized x-ray beam. Distinctively different angular distributions are observed for x-ray emission involving molecular orbitals of different symmetries. A classical model of the x-ray absorption-emission process accurately describes the observed radiation patterns.

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Molecular-Orbital Studies Via Satellite-Free X-Ray Fluorescence: Cl-K Absorption And K–Valence-Level Emission Spectra Of Chlorofluoromethanes, Rupert C. Perera, P. L. Cowan, Dennis W. Lindle, R. E. Lavilla, T. Jach, R. D. Deslattes Apr 1991

Molecular-Orbital Studies Via Satellite-Free X-Ray Fluorescence: Cl-K Absorption And K–Valence-Level Emission Spectra Of Chlorofluoromethanes, Rupert C. Perera, P. L. Cowan, Dennis W. Lindle, R. E. Lavilla, T. Jach, R. D. Deslattes

Chemistry and Biochemistry Faculty Research

X-ray absorption and emission measurements in the vicinity of the chlorine K edge of the three chlorofluoromethanes have been made using monochromatic synchrotron radiation as the source of excitation. By selectively tuning the incident radiation to just above the Cl 1s single-electron ionization threshold for each molecule, less complex x-ray-emission spectra are obtained. This reduction in complexity is attributed to the elimination of multielectron transitions in the Cl K shell, which commonly produce satellite features in x-ray emission. The resulting "satellite-free" x-ray-emission spectra exhibit peaks due only to electrons in valence molecular orbitals filling a single Cl 1s vacancy. These …

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Polarized X-Ray-Emission Studies Of Methyl Chloride And The Chlorofluoromethanes, Dennis W. Lindle, P. L. Cowan, T. Jach, R. E. Lavilla, R. D. Deslattes, Rupert C. Perera Mar 1991

Polarized X-Ray-Emission Studies Of Methyl Chloride And The Chlorofluoromethanes, Dennis W. Lindle, P. L. Cowan, T. Jach, R. E. Lavilla, R. D. Deslattes, Rupert C. Perera

Chemistry and Biochemistry Faculty Research

A new technique sensitive to molecular orientation and geometry, and based on measuring the polarization of x-ray emission, has been applied to the Cl-containing molecules methyl chloride (CH3Cl) and the chlorofluoromethanes (CF3Cl, CF2Cl2, and CFCl3) in the gas phase. Upon selective excitation using monochromatic synchrotron radiation in the Cl K-edge (Cl 1s) near-threshold region, polarization-selective x-ray emission studies reveal highly polarized molecular valence x-ray fluorescence for all four molecules. The degree and the orientation of the polarized emission are observed to be sensitive to the incident excitation energy near …

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Direct Determination Of Molecular-Orbital Symmetry Of H2s Using Polarized X-Ray Emission, R. Mayer, Dennis W. Lindle, S. H. Southworth, P. L. Cowan Jan 1991

Direct Determination Of Molecular-Orbital Symmetry Of H2s Using Polarized X-Ray Emission, R. Mayer, Dennis W. Lindle, S. H. Southworth, P. L. Cowan

Chemistry and Biochemistry Faculty Research

X-ray emission from the molecule H2S is strongly polarized following excitation of a sulfur K-shell electron to an unoccupied subthreshold molecular orbital with a polarized x-ray beam. Changes in the polarization of the emission spectrum are observed as the incident beam's energy is swept across the subthreshold absorption resonance. The previously unresolved absorption resonance is shown experimentally to be primarily associated with a molecular orbital of b2 symmetry, but with a high-excitation-energy component due to an orbital with a1 symmetry. Satellite emission intensity is shown to depend on the primary photon energy and is therefore associated …

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