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Articles 91 - 120 of 128
Full-Text Articles in Physical Sciences and Mathematics
An Injection-Locked Diode Laser For Cold Rydberg Atom Experiments, Margaret S. Martei, Anders P. Wood, Duncan A. Tate
An Injection-Locked Diode Laser For Cold Rydberg Atom Experiments, Margaret S. Martei, Anders P. Wood, Duncan A. Tate
Undergraduate Research Symposium (UGRS)
A free-running, temperature stabilized diode laser has been injection-locked to an external cavity diode laser for use in cold Rydberg atom experiments. Cold rubidium atoms in a magneto-optical trap (MOT) are excited to Rydberg states using a 10 ns laser pulse. The Rydberg atoms spontaneously ionize due to dipole forces, and the collisional ionization dynamics are observed as a function of atom density and principal quantum number of the Rydberg state, n. The injection-locked diode laser will be used as a repumper in conjunction with a dark spontaneous-force optical trap (SPOT) to increase the Rydberg state density. We report on …
Detection Of Al(Iii) And Ga(Iii) Complexes With Morin By Electrospray Ionization Mass Spectrometry, John B. Bremner, Larry A. Hick, Jody Morgan, Saowanee Rattanaphani, Vichitr Rattanaphani, C Septhum
Detection Of Al(Iii) And Ga(Iii) Complexes With Morin By Electrospray Ionization Mass Spectrometry, John B. Bremner, Larry A. Hick, Jody Morgan, Saowanee Rattanaphani, Vichitr Rattanaphani, C Septhum
Faculty of Science - Papers (Archive)
The Al(III) and Ga(III) complexes formed by morin (M) in aqueous solution were investigated by means of electrospray ionization mass spectrometry (ESI-MS). In the full scan mass spectra, Al:M showed 1:2 and 2:3 stoichiometric ratios. When (S)-N-acetylserine methyl ester (Ser), as a partial mimic of the serine residue in silk, was added to Al:M and Ga:M complexes in aqueous solution, the mass spectra of Ser:Al:M showed 1:1:1 and 1:1:2 stoichiometric ratios. The patterns of the mass spectra of Ga:M and Ser:Ga:M complexes were similar to those for the corresponding Al(III) complexes. Calculated heats of formation of potential structures of the …
Effect Of Protein Stabilization On Charge State Distribution In Positive- And Negative Ion Electrospray Ionization Mass Spectra, Stephen J. Watt, Margaret Sheil, Jennifer L. Beck, Pavel Prosselkov, Gottfried Otting, Nicholas E. Dixon
Effect Of Protein Stabilization On Charge State Distribution In Positive- And Negative Ion Electrospray Ionization Mass Spectra, Stephen J. Watt, Margaret Sheil, Jennifer L. Beck, Pavel Prosselkov, Gottfried Otting, Nicholas E. Dixon
Faculty of Science - Papers (Archive)
Changes in protein conformation are thought to alter charge state distributions observed in electrospray ionization mass spectra (ESI-MS) of proteins. In most cases, this has been demonstrated by unfolding proteins through acidification of the solution. This methodology changes the properties of the solvent so that changes in the ESI-MS charge envelopes from conformational changes are difficult to separate from the effects of changing solvent on the ionization process. A novel strategy is presented enabling comparison of ESI mass spectra of a folded and partially unfolded protein of the same amino acid sequence subjected to the same experimental protocols and conditions. …
Hydration Studies Of Electrospray Ions From Amino Acids And Small Peptides, Chuong Quoc Nguyen
Hydration Studies Of Electrospray Ions From Amino Acids And Small Peptides, Chuong Quoc Nguyen
Theses and Dissertations
This project was undertaken to gain a better understanding of the hydration behaviors of gas phase ions from solutions containing amino acids and peptides. In order to characterize their hydration behavior, the molecules of interest in solutions were first converted into gas phase ions by electrospray ionization (ESI). The completely desolvated ions were then deliberately dispersed into an inert bath gas, usually nitrogen, containing accurately known concentrations of solvent vapor. The resulting mixtures of ions and bath gas were subsequently passed into a vacuum chamber by way of an adiabatic supersonic free jet expansion. The cooling during that expansion caused …
Differential Electron Emission For Single And Multiple Ionization Of Argon By 500 Ev Positrons, Jared M. Gavin, Robert D. Dubois, O. G. De Lucio
Differential Electron Emission For Single And Multiple Ionization Of Argon By 500 Ev Positrons, Jared M. Gavin, Robert D. Dubois, O. G. De Lucio
Physics Faculty Research & Creative Works
Triply differential electron emission cross sections are measured for single ionization of argon by 500 eV positrons. Data are presented for coincidences between projectiles scattered into angles of 3° and electrons with emission energies less than 10 eV that are observed between 45 and 135° along the beam direction. For interpretation, these are compared to cosine squared representations of the binary and recoil lobes which are convoluted over experimental parameters. Singly differential electron emission data for double and triple ionization by positrons are also presented.
Analysis Of Two-Dimensional Photoelectron Momentum Spectra And The Effect Of The Long-Range Coulomb Potential In Single Ionization Of Atoms By Intense Lasers, Zhangjin Chen, Toru Morishita, Anh-Thu Le, M. Wickenhauser, X. M. Tong, C. D. Lin
Analysis Of Two-Dimensional Photoelectron Momentum Spectra And The Effect Of The Long-Range Coulomb Potential In Single Ionization Of Atoms By Intense Lasers, Zhangjin Chen, Toru Morishita, Anh-Thu Le, M. Wickenhauser, X. M. Tong, C. D. Lin
Physics Faculty Research & Creative Works
Two-dimensional (2D) electron momentum distributions and energy spectra for multiphoton ionization of atoms by intense laser pulses, calculated by solving the time-dependent Schrödinger equation (TDSE) for different wavelengths and intensities, are compared to those predicted by the strong-field approximation (SFA). It is shown that the momentum spectra at low energies between the TDSE and SFA are quite different and the differences arise largely from the absence of a long-range Coulomb interaction in the SFA. We further found that the low-energy 2D momentum spectra from the TDSE exhibit ubiquitous fanlike features where the number of stripes is due to a single …
(E,2e) Measurements On Xenon: Reexamination Of The Fine-Structure Effect, Radmila Panajotovic, Julian C A Lower, Erich Weigold, A. Prideaux, Don H. Madison
(E,2e) Measurements On Xenon: Reexamination Of The Fine-Structure Effect, Radmila Panajotovic, Julian C A Lower, Erich Weigold, A. Prideaux, Don H. Madison
Physics Faculty Research & Creative Works
The process of electron scattering from heavy target atoms is of considerable interest due to the enhanced role of relativistic effects and distortion of the electron trajectories resulting from the large value of nuclear charge. Here we present (e,2e) ionization measurements and distorted-wave Born approximation calculations for the scattering of spin-polarized electrons from xenon atoms in which the fine-structure levels of the residual ion are resolved. Comparison of measurements performed using a high-sensitivity toroidal analyzer spectrometer with the predictions of sophisticated calculations provide an improved understanding of the ionization dynamics of heavy target atoms and the treatment of electron exchange …
Two-Photon Excitation Dynamics In Bound Two-Body Coulomb Systems Including Ac Stark Shift And Ionization, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel, Nikolai N. Kolachevsky, Maximilian Herrmann, Peter Fendel, Marc P. Fischer, Th H. Udem, Ronald Holzwarth, Theodor Wolfgang Hansch, Marlan O. Scully, Girish S. Agarwal
Two-Photon Excitation Dynamics In Bound Two-Body Coulomb Systems Including Ac Stark Shift And Ionization, Martin K. Haas, Ulrich D. Jentschura, Christoph H. Keitel, Nikolai N. Kolachevsky, Maximilian Herrmann, Peter Fendel, Marc P. Fischer, Th H. Udem, Ronald Holzwarth, Theodor Wolfgang Hansch, Marlan O. Scully, Girish S. Agarwal
Physics Faculty Research & Creative Works
One of the dominant systematic effects that shift resonance lines in high-precision measurements of two-photon transitions is the dynamic (ac) Stark shift. For suitable laser frequencies, the ac Stark shift acquires an imaginary part which corresponds to the rate of resonant one-photon ionization of electrons into a continuum state. At the current level of spectroscopic accuracy, the underlying time-dependent quantum dynamics governing the atomic two-photon excitation process must be well understood, and related considerations are the subject of the present paper. In order to illustrate the basic mechanisms in the transient regime, we investigate an analytically solvable model scenario for …
Evidence Of Two-Center Interference In High-Order Harmonic Generation From Co₂, Anh-Thu Le, Xiao-Min Tong, C. D. Lin
Evidence Of Two-Center Interference In High-Order Harmonic Generation From Co₂, Anh-Thu Le, Xiao-Min Tong, C. D. Lin
Physics Faculty Research & Creative Works
Two recent pump-probe experiments on the high-order harmonic generation (HHG) from partially aligned CO₂ molecules have shown that the HHG yields versus the ionization rates as functions of the pump-probe delay time exhibit inverted modulation. The inversion has been attributed to the quantum interference in the recombination process from the two oxygen centers. Using the Lewenstein model to calculate HHG from fixed CO₂ molecules and taking into account the partial alignment of the molecules versus the time delay, we interpret that the inversion is due to the degree of overlap between the partially aligned molecules and the angular dependence of …
Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich
Mutual Ionization In 200-Kev H⁻+ He Collisions, T. Ferger, Daniel Fischer, Michael Schulz, R. Moshammer, A. B. Voitkiv, B. Najjari, J. Ullrich
Physics Faculty Research & Creative Works
We studied mutual ionization in 200-keV H-+He collisions in a kinematically complete experiment by measuring the fully momentum-analyzed recoil ions and both active electrons in coincidence. Comparison of the data to our calculations, based on various theoretical models, show that mutual ionization proceeds predominantly through the interaction between both electrons. The post-collision interaction between the outgoing ejected electrons as well as higher order processes involving the interaction between the core of both collision partners are also important.
Performance Of Binary-Encounter-Bethe (Beb) Theory For Electron-Impact Ionization Cross Sections Of Molecules Containing Heavy Elements (Z > 10), Gregory E. Scott, Karl K. Irikura
Performance Of Binary-Encounter-Bethe (Beb) Theory For Electron-Impact Ionization Cross Sections Of Molecules Containing Heavy Elements (Z > 10), Gregory E. Scott, Karl K. Irikura
Chemistry and Biochemistry
The binary-encounter-Bethe (BEB) theory developed by Kim and coworkers has been successful for computing electron-impact ionization cross sections of many molecules. However, some recent publications have stated that BEB theory performs poorly for molecules that contain heavier elements such as chlorine and sulfur. We have found that the BEB calculations in those publications were performed incorrectly. When performed correctly, BEB predictions are as good for heavy-element molecules as for light-element molecules. We recommended recently that an alternative, less-confusing procedure be used for molecules that contain heavier elements. The alternative procedure, based upon effective core potentials (ECPs), does not require explicit …
Kinetic, Spectroscopic, And X-Ray Crystallographic Characterization Of The Functional E151h Aminopeptidase From Aeromonas Proteolytica, Krzysztof P. Bzymek, Aaron Moulin, Sabina I. Swierczek, Dagmar Ringe, Gregory A. Petsko, Brian Bennett, Richard C. Holz
Kinetic, Spectroscopic, And X-Ray Crystallographic Characterization Of The Functional E151h Aminopeptidase From Aeromonas Proteolytica, Krzysztof P. Bzymek, Aaron Moulin, Sabina I. Swierczek, Dagmar Ringe, Gregory A. Petsko, Brian Bennett, Richard C. Holz
Physics Faculty Research and Publications
Glutamate151 (E151) has been shown to be catalytically essential for the aminopeptidase from Vibrio proteolyticus (AAP). E151 acts as the general acid/base during the catalytic mechanism of peptide hydrolysis. However, a glutamate residue is not the only residue capable of functioning as a general acid/base during catalysis for dinuclear metallohydrolases. Recent crystallographic characterization of the d-aminopeptidase from Bacillus subtilis (DppA) revealed a histidine residue that resides in an identical position to E151 in AAP. Because the active-site ligands for DppA and AAP are identical, AAP has been used as a model enzyme to understand the mechanistic role of H115 in …
Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin
Signature Of Chaos In High-Lying Doubly Excited States Of The Helium Atom, Anh-Thu Le, Toru Morishita, X.-M. Tong, C. D. Lin
Physics Faculty Research & Creative Works
We examined nearest-neighbor spacing (NNS) statistics in doubly excited states of helium near the double ionization threshold. Using the Brody parameter q to measure the NNS distribution between the regular Poisson distribution (q=0) and the chaotic Wigner distribution (q=1), we showed that for levels near the N=20 threshold of He⁺, or at about 0.13eV below the double ionization threshold, the NNS distribution has q=0.66. The result shows the slow approach of the NNS of helium energy levels towards the Wigner distribution vs the excitation energy. Using an s-wave model where the angular momentum of each electron is restricted to zero, …
Analysis Of Adsorbed Contaminants Of Caf/Sub 2/ Surfaces By Infrared Laser Induced Desorption, Jinmei Fu, Yamini Surapaneni, Susan D. Allen
Analysis Of Adsorbed Contaminants Of Caf/Sub 2/ Surfaces By Infrared Laser Induced Desorption, Jinmei Fu, Yamini Surapaneni, Susan D. Allen
Mechanical Engineering - Daytona Beach
157 nm photolithography technologies are currently under development and have been accepted as the leading candidate for fabrication of the next generation semiconductor devices after 193 nm. At this and shorter wavelengths, molecular contamination of surfaces becomes a serious problem as almost all molecules absorb at 157 nm and below. The light transmitted by a photolithographic tool can be significantly decreased by the presence of a few monolayers adsorbed on its many optical surfaces. We have developed a laser induced desorption, electron impact ionization, time-of-flight mass spectrometer (LID TOFMS) to study contaminants on 157nm and other ultraviolet optics, e.g., polished …
Breakup Of H₂ In Singly Ionizing Collisions With Fast Protons: Channel-Selective Low-Energy Electron Spectra, Christina Dimopoulou, Robert Moshammer, Daniel Fischer, C. Hohr, Alexander Dorn, Pablo Daniel Fainstein, Jose R. Crespo Lopez-Urrutia, Claus Dieter Schroter, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich
Breakup Of H₂ In Singly Ionizing Collisions With Fast Protons: Channel-Selective Low-Energy Electron Spectra, Christina Dimopoulou, Robert Moshammer, Daniel Fischer, C. Hohr, Alexander Dorn, Pablo Daniel Fainstein, Jose R. Crespo Lopez-Urrutia, Claus Dieter Schroter, Holger Kollmus, Rido Mann, Siegbert Hagmann, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
The dissociation of H2 in singly ionizing collisions with fast protons was analyzed using channel-selective low-energy electron spectra. Dissociative and nondissociative single ionization of H2 by 6MeV proton impact was described in a kinematically by determining momentum vectors of electron and H+ fragment of H2+ target ion, respectively. The electron spectra exhibited role of autoionization of doubly and singly excited states of H2. The doubly and singly excited states of H2 involve coupling between electronic and nuclear motion of molecule.
Probing Scattering Wave Functions Close To The Nucleus, Don H. Madison, Daniel Fischer, Matthew S. Foster, Michael Schulz, Robert Moshammer, Stephenie J. Jones, Joachim Hermann Ullrich
Probing Scattering Wave Functions Close To The Nucleus, Don H. Madison, Daniel Fischer, Matthew S. Foster, Michael Schulz, Robert Moshammer, Stephenie J. Jones, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
Recently, three-dimensional imaging of the ejected electrons following 100 MeV/amu C6+ single ionization of helium led to the observation of a new structure not predicted by theory [M. Schulz et al., Nature (London) 422, 48 (2003)]. Instead of the usual “recoil lobe” centered on the momentum-transfer axis, a ring-shaped structure centered on the beam axis was observed. New measurements at 2 MeV/amu exhibit a similar structure, which is now predicted by theory. We argue that the same theory failed at 100 MeV/amu because the faster projectiles probe distances much closer to the nucleus, where our multiple-scattering model is expected …
Rescattering Of Ultralow-Energy Electrons For Single Ionization Of Ne In The Tunneling Regime, Robert Moshammer, Joachim Hermann Ullrich, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, Jose R. Crespo Lopez-Urrutia, C. Hoehr, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner
Rescattering Of Ultralow-Energy Electrons For Single Ionization Of Ne In The Tunneling Regime, Robert Moshammer, Joachim Hermann Ullrich, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, Jose R. Crespo Lopez-Urrutia, C. Hoehr, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner
Physics Faculty Research & Creative Works
Electron emission for single ionization of Ne by 25 fs, 1.0 PW/cm2 laser pulses at 800 nm was investigated. Kinematics was studied using a 'reaction microscope'. Results showed a zero longitudinal momentum of a low-energy electron with high resolution.
Simultaneous Projectile-Target Ionization: A Novel Approach To (E, 2e) Experiments On Ions, Holger Kollmus, Robert Moshammer, Ronald E. Olson, Siegbert Hagmann, Michael Schulz, Joachim Hermann Ullrich
Simultaneous Projectile-Target Ionization: A Novel Approach To (E, 2e) Experiments On Ions, Holger Kollmus, Robert Moshammer, Ronald E. Olson, Siegbert Hagmann, Michael Schulz, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
A kinematically complete experiment for simultaneous ionization of a projectile and target has been performed for 3.6 MeV/u C2+ on He collisions measuring the final vector momenta of the He1+ recoil ion and of two electrons (projectile, target) in coincidence with the emerging C3+ projectile. The feasibility of an event-by-event separation of the various reaction channels, among them the ionization of C2+ by the interaction with a quasifree target electron, is demonstrated in agreement with six-body classical trajectory Monte Carlo calculations, paving the way to kinematically complete electron-ion scattering experiments.
Separation Of Recollision Mechanisms In Nonsequential Strong Field Double Ionization Of Ar: The Role Of Excitation Tunneling, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Joachim Hermann Ullrich
Separation Of Recollision Mechanisms In Nonsequential Strong Field Double Ionization Of Ar: The Role Of Excitation Tunneling, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner, Robert Moshammer, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25PW/cm2 laser pulses at 795 nm have been measured using a “reaction microscope.” At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical “recollision model” revealed an (e,2e)-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization yield.
Non-Sequential Double Ionization Of Ne In Intense Laser Pulses: A Coincidence Experiment, Robert Moshammer, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Joachim Hermann Ullrich, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner
Non-Sequential Double Ionization Of Ne In Intense Laser Pulses: A Coincidence Experiment, Robert Moshammer, Bernold Feuerstein, Daniel Fischer, Alexander Dorn, Claus Dieter Schroter, J. Deipenwisch, Jose R. Crespo Lopez-Urrutia, C. Hohr, Paul B. Neumayer, Joachim Hermann Ullrich, Horst Rottke, Christoph Trump, M. Wittmann, Georg Korn, Wolfgang Sandner
Physics Faculty Research & Creative Works
The dynamics of Neon double ionization by 25 fs, 1.0 PW/cm2 laser pulses at 795 nm has been studied in a many particle coincidence experiment. The momentum vectors of all ejected atomic fragments (electrons and ions) have been measured using combined electron and recoil-ion momentum spectroscopy. Electron emission spectra for double and single ionization will be discussed. In both processes the mean electron energies differ considerably and high energetic electrons with energies of more than 120 eV have been observed for double ionization. The experimental results are in qualitative agreement with the rescattering model.
Fully Differential Cusp Electron Production Cross Sections For 75-Kev H₂⁺ + He Collisions, L. An, Kh Khayvat, Michael Schulz
Fully Differential Cusp Electron Production Cross Sections For 75-Kev H₂⁺ + He Collisions, L. An, Kh Khayvat, Michael Schulz
Physics Faculty Research & Creative Works
A kinematically complete experiment on single ionization for 75-keV H2+ + H e collisions was performed by measuring the fully momentum analyzed projectiles and recoil ions in coincidence. The electron momentum was deduced from momentum conservation. Clear signatures of the postcollision interaction between the outgoing projectiles and the electrons were observed in the momentum spectra of all collision products simultaneously.
Electron Heating In Atmospheric Pressure Glow Discharges, Robert H. Stark, Karl H. Schoenbach
Electron Heating In Atmospheric Pressure Glow Discharges, Robert H. Stark, Karl H. Schoenbach
Bioelectrics Publications
The application of nanosecond voltage pulses to weakly ionized atmospheric pressure plasmas allows heating the electrons without considerably increasing the gas temperature, provided that the duration of the pulses is less than the critical time for the development of glow-to-arc transitions. The shift in the electron energy distribution towards higher energies causes a temporary increase in the ionization rate, and consequently a strong rise in electron density. This increase in electron density is reflected in an increased decay time of the plasma after the pulse application. Experiments in atmospheric pressure air glow discharges with gas temperatures of approximately 2000 K …
Electric Field Controlled, Pulsed Autoionization In Two Electron Wave Packets, J. Greg Story, Heider N. Ereifej
Electric Field Controlled, Pulsed Autoionization In Two Electron Wave Packets, J. Greg Story, Heider N. Ereifej
Physics Faculty Research & Creative Works
In this paper, control of the evolution of a two electron wave packet through the application of a static electric field is demonstrated. Specifically, application of a small electric field is used to produce pulsed autoionization events, the timing of which can be controlled on a picosecond time scale. The technique is demonstrated by exciting calcium atoms using a short-pulsed laser to the 4p3/219d doubly excited state, which is energy degenerate with the 4p1/2nk stark states. Evolution of the resultant wave packet is monitored through the application of a second short laser pulse, which stimulates the …
An Incoherent Scatter Radar Technique For Determining Two-Dimensional Ionization Structure In Polar Cap F-Region Patches, T. R. Pedersen, Bela G. Fejer, R. A. Doe, E. J. Weber
An Incoherent Scatter Radar Technique For Determining Two-Dimensional Ionization Structure In Polar Cap F-Region Patches, T. R. Pedersen, Bela G. Fejer, R. A. Doe, E. J. Weber
Bela G. Fejer
We present a technique which combines time series of line-of-sight (LOS) velocity and electron density measurements from the Sondrestrom incoherent scatter radar (74.5° invariant latitude) to reconstruct the large-scale horizontal structure of the F region ionosphere during polar cap patch events. This reconstruction technique provides a new density-based means of examining patch morphology. Its wide region of coverage also facilitates comparison of radar measurements with other observational data sets. For two periods when patches were present and convection conditions in the nightside polar cap could be adequately approximated by the simple velocity model used in this initial implementation of the …
Photofragmentation Of Third-Row Hydrides Following Photoexcitation At Deep-Core Levels, D. L. 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
Photofragmentation Of Third-Row Hydrides Following Photoexcitation At Deep-Core Levels, D. L. 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
X-Ray Atomic and Molecular Science Program
The relaxation dynamics of HCl, DCl, H2S, and D2S following photoexcitation in the vicinities of the Cl and S K-shell thresholds (~2.8 keV 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, …
Auger Resonance Decay Process In Ar 2p Shell Excitation And Ionization, Y. Lu, Wayne C. Stolte, J.A. R. Samson
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.
Double Photoionization Of Helium, James A.R. Samson, Wayne C. Stolte, Z. X. He, Y. Lu, J. N. Cutler, R. J. Bartlett
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.
Time-Resolved Studies Of Ultracold Ionizing Collisions, Scott D. Bergeson, C. Orzel, S. Kulin, S. L. Rolston
Time-Resolved Studies Of Ultracold Ionizing Collisions, Scott D. Bergeson, C. Orzel, S. Kulin, S. L. Rolston
Faculty Publications
Using 40 ns laser pulses, we probe the real-time dynamics of ultracold ionizing collisions in metastable xenon. We time resolve both shielding and enhancement effects, and observe the production of Xe2^+ molecular ions through associative ionization. We estimate the rate of molecule formation in excited-state collisions, and directly measure the role of both flux enhancement and excited state survival in the collisional enhancement process. Conceptually simple theoretical models are used to predict the dynamics of the collisional shielding.
Grains In Ionized Nebulae: Spectral Line Diagnostics, J. B. Kingdon, Gary J. Ferland, W. A. Feibelman
Grains In Ionized Nebulae: Spectral Line Diagnostics, J. B. Kingdon, Gary J. Ferland, W. A. Feibelman
Physics and Astronomy Faculty Publications
The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the [Ca II] λλ7291, 7324 doublet and the detection of …
Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher
Landau-Zener Treatment Of Intensity-Tuned Multiphoton Resonances Of Potassium, J. Greg Story, D. I. Duncan, Thomas F. Gallagher
Physics Faculty Research & Creative Works
When exposed to intense light of ~580 nm, the ground state of K shifts up in energy, passing through two photon resonances with Rydberg states, and finally crossing the two-photon ionization limit. We have used laser pulses of varying duration to study the nature of the population transfer from the ground state to the excited state due to the intensity-tuned resonances encountered during the rising edge of the pulse. A dynamic Floquet approach in which the resonances are treated as avoided crossings of the Floquet energy levels is used to model the population transfer and gives excellent agreement with the …