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Grid-based methods for diatomic quantum scattering problems III: Double photoionization of molecular hydrogen in prolate spheroidal coordinates

Description: Our previously developed finite-element/ discrete variable representation in prolate spheroidal coordinates is extended to two-electron systems with a study of double ionization of H$_2$ with fixed-nuclei. Particular attention is paid to the development of fast and accurate methods for treating the electron-electron interaction. The use of exterior complex scaling in the implementation offers a simple way of enforcing Coulomb boundary conditions for the electronic double continuum. While the angular distributions calculated in this study are found to be completely consistent with our earlier treatments that employed single-center expansions in spherical coordinates, we find that the magnitude of the integrated cross sections are sensitive to small changes in the initial-state wave function. The present formulation offers significant advantages with respect to convergence and efficiency and opens the way to calculations on more complicated diatomic targets.
Date: June 10, 2010
Creator: Tao, Liang; McCurdy, Bill & Rescigno, Tom
Partner: UNT Libraries Government Documents Department


Description: Equations providing the first and second derivatives of a configuration interaction (CI) energy with respect to an external parameter are provided. We assume no restriction on the form of the CI expansion built from molecular orbitals obtained in a multiconfiguration Hartree-Fock (MCHF) calculation. Also the coupled perturbed multi-configuration Hartree-Fock formalism is presented for a general MCHF wavefunction and provides the first order and second order changes of the molecular orbital expansion coefficients with respect to an external parameter.
Date: September 1, 1980
Creator: Dupuis, M.
Partner: UNT Libraries Government Documents Department

Vibrational Feshbach resonances in near threshold HOCO{sup -} photodetachment: a theoretical study

Description: The results of a theoretical study of HOCO{sup −} photodetachment are presented, with a view toward understanding the origin of two peaks observed by Lu and Continetti (Phys. Rev. Lett. 99, 113005 (2007)) in the photoelectron kinetic energy spectrum very close to threshold. It is shown that the peaks can be attributed to vibrational Feshbach resonances of dipole-bound trans-HOCO{sup −}, and not s- and p-wave shape resonances as previously assumed. Fixed-nuclei variational electron-HOCO scattering calculations are used to compute photodetachment cross sections and laboratory-frame photoelectron angular distributions. The calculations show a broad A′′(#25;{pi}*)-shape resonance several eV above threshold.
Date: March 2, 2011
Creator: Miyabe, Shungo; Haxton, Dan; Lawler, Keith; Orel, Ann; McCurdy, Bill & Rescigno, Tom
Partner: UNT Libraries Government Documents Department

Role of nuclear dynamics in the Asymmetric molecular-frame photoelectron angular distributions for C 1s photoejection from CO{sub 2}

Description: We report the results of semiclassical calculations of the asymmetric molecular-frame photoelectron angular distributions for C 1s ionization of CO{sub 2} measured with respect to the CO{sup +} and O{sup +} ions produced by subsequent Auger decay, and show how the decay event can be used to probe ultrafast molecular dynamics of the transient cation. The fixed-nuclei photoionization amplitudes were constructed using variationally obtained electron-molecular ion scattering wave functions. The amplitudes are then used in a semiclassical manner to investigate their dependence on the nuclear dynamics of the cation. The method introduced here can be used to study other core-level ionization events.
Date: November 30, 2010
Creator: Miyabe, Shungo; Haxton, Dan; Rescigno, Tom & McCurdy, Bill
Partner: UNT Libraries Government Documents Department


Description: The purpose of this letter is to call attention to a growing misinterpretation in the literature on rainbow scattering in inelastic molecular collisions. The importance of rainbow structures in the angular distributions of elastic scattering cross sections is well established. However, use of approximate cross section formulas has led to an incorrect classification of the types of rainbows which are possible. Actually, however, it is possible to identify two classes of rainbows. If the relevant distributions and classifications are clearly stated, there should be little chance of confusion,
Date: May 1, 1980
Creator: Thomas, L.D.
Partner: UNT Libraries Government Documents Department

Dissociative Electron Attachment to Carbon Dioxide via the 8.2 eV Feshbach resonance

Description: Momentum imaging experiments on dissociative electron attachment (DEA) to CO{sub 2} are combined with the results of ab initio calculations to provide a detailed and consistent picture of the dissociation dynamics through the 8.2 eV resonance, which is the major channel for DEA in CO{sub 2}. The present study resolves several puzzling misconceptions about this system.
Date: August 17, 2011
Creator: Slaughter, Dan; Adaniya, Hidihito; Rescigno, Tom; Haxton, Dan; Orel, Ann; McCurdy, Bill et al.
Partner: UNT Libraries Government Documents Department

Observation of the dynamics leading to a conical intersection in dissociative electron attachment to water

Description: Following prior work on the lower-energy resonances, we apply techniques of momentum imaging and ab initio scattering calculations to the process of dissociative electron attachment to water via the highest-energy {sup 2}B{sub 2} resonance. We focus on the H{sup -} anion fragment, which is produced via dynamics passing through and avoiding the conical intersection with the lower A{sub 1} state, leading to OH ((sup 2}{Pi}#5;) and OH ({sup 2}{Sigma}#6;), respectively. The momentum imaging technique, when combined with theoretical calculations on the attachment amplitude and dissociation dynamics, demonstrates that the angular distributions provide a signature of the location of the conical intersection in the space of nuclear con#12;gurations.
Date: June 8, 2011
Creator: Haxton, Dan; Adaniya, Hidihito; Slaughter, Dan; Rudek, B.; Osipov, Timur; Weber, Thorsten et al.
Partner: UNT Libraries Government Documents Department


Description: The Vibrational Spectroscopy conference brings together experimentalists and theoreticians working at the frontiers of modern vibrational spectroscopy, with a special emphasis on spectroscopies that probe the structure and dynamics of molecules in gases, liquids, and at interfaces. The conference explores the wide range of state-of-the-art techniques based on vibrational motion. These techniques span the fields of time-domain, high-resolution frequency-domain, spatially-resolved, nonlinear, and multidimensional spectroscopies. The conference highlights both the application of these techniques in chemistry, materials, biology, the environment, and medicine as well as the development of theoretical models that enable one to connect spectroscopic signatures to underlying molecular motions including chemical reaction dynamics. The conference goal is to advance the field of vibrational spectroscopy by bringing together a collection of researchers who share common interests and who will gain from discussing work at the forefront of several connected areas. The intent is to emphasize the insights and understanding that studies of vibrations provide about a variety of molecular systems ranging from small polyatomic molecules to large biomolecules, nanomaterials, and environmental systems.
Date: August 10, 2012
Creator: Geiger, Franz
Partner: UNT Libraries Government Documents Department


Description: To study rotational excitations of CO by He impact, configurationinteraction potential energy surfaces have been computed with two different basis sets. The surfaces are compared to one another, to an electron-gas surface, and to an experimentally determined surface. In addition, converged close-coupling calculations of the collision cross sections have been done on these surfaces for energies up to 100 cm{sup -1} and compared. On the most accurate CI surface, cross sections have been computed using the infinite-order sudden (IOS) and quasi-classical methods as well.
Date: March 1, 1980
Creator: Thomas, L.D.; Kraemer, W.P. & Diercksen, G.H.F.
Partner: UNT Libraries Government Documents Department


Description: A systematic investigation of K x-ray production for 20-80 MeV Cl ions in collision with thin self-supporting Cu targets has been conducted. Target and projectile characteristic x rays and radiative electron capture (REC) have been measured as a function of target thickness for incident charge states q < z{sub 1} - 2. At 80 MeV data were also obtained for q = z{sub 1}- 1. Large enhancements in both characteristic x-ray production and REC were observed for q = z{sub 1}- 1. Measured x-ray yields were parametrized vs. target thickness using the model of Betz et al. and least squares fits to the data were performed. Target K x-ray production for q<z{sub 1}-2 is described reasonably well by the CPSSR + ECR theory. For q=z{sub 1} - 1 the enhancement in the x-ray yield is predicted quite well by the method of Gray et al· The mean fluorescence yield for the highly stripped Cl ions is determined and found to increase by a factor of about six over the range 20-80 MeV, having a value (~0.1) nearly equal to the single K-vacancy value at 20 MeV. The radiative lifetime for the projectile ions is found to be ~3 x 10{sup -14} sec which is about three times longer than the single K-vacancy radiative lifetime calculated by Scofield. Parametrization of the REC yields vs. target thickness is used to normalize the measured REC intensity to the fraction of ions with K vacancies. Resulting REC cross sections are compared with the free-electron theory of Bethe and Salpeter and good agreement is obtained if it is assumed that each of the "loosely" bound electrons in Cu contributes equally to the REC process. By combining the results obtained for the characteristic x rays and REC, the fluorescence yield for K-shell capture events may be ...
Date: December 1, 1980
Creator: Tanis, J.A.; Jacobs, W.W. & Shafroth, S.M.
Partner: UNT Libraries Government Documents Department


Description: The range of experimental confirmation of our scaling rule for electron loss from a hydroqen atom in collision with a heavy, highly stripped ion has been considerably broadened by new measurements for carbon, niobium, and lead ions in molecular hydrogen.
Date: November 1, 1980
Creator: Schlachter, A. S.; Berkner, K. H.; Graham, W. G.; Pyle, R. V.; Stearns, J. W. & Tanis, J. A.
Partner: UNT Libraries Government Documents Department


Description: The dependence of projectile double K-vacancy (hypersatellite) x-ray yields on target thickness for ions moving in thin solid targets is examined. For 2.3 MeV/amu Cl ions incident on C foils, the double-to-single K vacancy x-ray yield increases by a factor of 3.5 over the range of thicknesses investigated, reaching values as high as 30%. A quantitative explanation of the observed results is obtained using the three-component model of Gardner et al.
Date: January 1, 1980
Creator: Tanis, J.A.; Shafroth, S.M.; Willis, J.E. & Mowat, J.R.
Partner: UNT Libraries Government Documents Department


Description: We have determined the net ionization cross section for total slow-ion or slow-electron charge production in rare-gas targets by passage of a fast projectile both experimentally and theoretically. We have experimentally studied ionization in these targets by C, Fe, Nb, and Pb projectiles with energies ranging from 310 keV/amu to 4.8 MeV/amu and for charge states in the range of +4 to +54. Theoretical calculations employing the classical-trajectory Monte-Carlo method are used to calculate ionization cross sections in the rare gases for projectiles at collision energies of 1 MeV/amu to 5 MeV/amu with charge states +5 to +80. Experiment and theory generally agree within a factor of 2 over this wide range of conditions. For a given rare-gas target, the cross sections for net ionization reduce to a common curve when plotted as cross section divided by charge state versus energy per nucleon divided by charge state.
Date: October 1, 1980
Creator: Schlachter, A.S.; Berkner, K.H.; Graham, W.G.; Pyle, R.V.; Schneider, P.J.; Stadler, K.R. et al.
Partner: UNT Libraries Government Documents Department

Classical Model for Electronically Non-Adiabatic Collision Processes: Resonance Effects in Electronic-Vibrational Energy Transfer

Description: A recently developed classical model for electronically nonadiabatic collision processes is applied to electronic-vibrational energy transfer in a collinear atom~diatom system, A + BC(v=1) + A*+ BC(v=0), which closely resembles Br-H{sub 2}. This classical model, which treats electronic as well as heavy particle (i.e., translation, rotation, and vibration) degrees of freedom by classical mechanics, is found to describe the resonance features in this process reasonably well. The usefulness of the approach is that it allows one to extend standard Monte Carlo classical trajectory methodology to include electronically non-adiabatic processes in a dynamically consistent way,
Date: November 1, 1980
Creator: Orel, Ann E. & Miller, William H.
Partner: UNT Libraries Government Documents Department

Design of a Molecular Beam Surface Scattering Apparatus for Velocity and Angular Distribution Measurements

Description: A molecular beam surface scattering apparatus designed for the study of corrosion and catalyticsurfacereactions is described. The apparatus incorporates two molecular or atomic beams aimed at a surface characterized by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES), a rotatable, differentially pumped quadrupole mass spectrometer, and a versatile manipulator. Angular distributions and energy distributions as a funcion of angle and independent of the surface residence time can be measured. Typical data for the oxidation of deuterium to D{sub 2}O on a Pt(lll) crystal surface are presented.
Date: November 1, 1980
Creator: Ceyer, S. T.; Siekhaus, W. J. & Somorjai, G. A.
Partner: UNT Libraries Government Documents Department

Fluorescence of Optically Pumped Trapped Ions

Description: Narrow bandwidth laser excitation of the 2 {sup 3}s{sub 1} {yields} 2 {sup 3}P{sub J} (J= 0,1,2) transitions near 5485 {Angstrom} from 2 {sup 3}S{sub 1} Li{sup +} ions confined in an rf quadrupole trap has produced novel fluorescence response curves (fluorescence vs. laser frequency) characteristic of optical pumping in the absence of strong hyperfine relaxation. The 2 {sup 3}S{sub 1} {yields} 2 {sup 3}P{sub 2,1} transitions in 7Li{sup +} were extensively studied. The observations are consistent with predictions of a rate equation model which treats the ions as a gas in temperature equilibrium. A narrow bandwidth pumping source (Iinewidth < Doppler width and hyperfine splittings) produces a response curve narrower than the Doppler blended hyperfine complex. Frequency scanning elicits hysteresis effects when the scan rate exceeds the response rate of the pumped ions.
Date: March 1, 1980
Creator: Prior, M. H. & Knight, R. D.
Partner: UNT Libraries Government Documents Department

Evidence for Photodissociation of Water Vapor on Reduced SrTiO{Sub 3}(111) Surfaces in a High Vacuum Environment. Relationship Between the Rate of Hydrogen Evolution and the Surface Concentration of Ti{Sup 3+} Species

Description: We have observed D{sub 2} photoproduction from D{sub 2}O vapor at a pressure of ~1x10{sup -7} Torr on a reduced SrTiO{sub 3} (111) crystal face at a temperature of ~600 K. Electron loss spectoscopy data showed a decrease in the surface concentration of Ti{sup 3+} species while the crystal face was being illuminated and the D{sub 2} photoproduced, indicating that the oxygen was being incorporated into the crystal lattice.
Date: August 1, 1980
Creator: Ferrer, S. & Somorjai, G. A.
Partner: UNT Libraries Government Documents Department

Electron Capture by Trapped Ne{Sup 10+} at Very Low Energies

Description: An electrostatic ion trap has been used to trap Ne{sup q+} (1{<=}q{<=}10) ions created by a fast xenon beam passing through neon gas. Exponential decay in time of the Ne{sup 10+} fraction due to electron capture from neon gas was observed and the decay rates measured. For mean kinetic energies between 7-45 eV, the total electron capture cross section ({sigma}{sub e.c}) is found to be velocity independent. For this energy range we obtain {sigma}{sub e.c}(Ne{sup 10+}) = 2.4 x 10{sup -15} cm{sup 2} , with an estimated uncertainty of 30 percent.
Date: September 1, 1980
Creator: Vane, C. R.; Prior, M. H. & Marrus, Richard
Partner: UNT Libraries Government Documents Department

The Application of Some Hartree-Fock Model Calculation to the Analysis of Atomic and Free-Ion Optical Spectra

Description: Techniques for applying ab-initio calculations to the is of atomic spectra are investigated, along with the relationship between the semi-empirical and ab-initio forms of Slater-Condon theory. Slater-Condon theory is reviewed with a focus on the essential features that lead to the effective Hamiltonians associated with the semi-empirical form of the theory. Ab-initio spectroscopic parameters are calculated from wavefunctions obtained via self-consistent field methods, while multi-configuration Hamiltonian matrices are constructed and diagonalized with computer codes written by Robert Cowan of Los Alamos Scientific Laboratory. Group theoretical analysis demonstrates that wavefunctions more general than Slater determinants (i.e. wavefunctions with radial correlations between electrons) lead to essentially the same parameterization of effective Hamiltonians. In the spirit of this analysis, a strategy is developed for adjusting ab-initio values of the spectroscopic parameters, reproducing parameters obtained by fitting the corresponding effective Hamiltonian. Secondary parameters are used to "screen" the calculated (primary) spectroscopic parameters, their values determined by least squares. Extrapolations of the secondary parameters determined from analyzed spectra are attempted to correct calculations of atoms and ions without experimental levels. The adjustment strategy and extrapolations are tested on the K I sequence from K{sup 0+} through Fe{sup 7+}, fitting to experimental levels for V{sup 4+}, and Cr{sup 5+}; unobserved levels and spectra are predicted for several members of the sequence. A related problem is also discussed: Energy levels of the Uranium hexahalide complexes, (UX{sub 6}){sup 2-} for X= F, Cl, Br, and I, are fit to an effective Hamiltonian (the f{sup 2} configuration in O{sub h} symmetry) with corrections proposed by Brian Judd.
Date: August 6, 1980
Creator: Hayhurst, Thomas Laine
Partner: UNT Libraries Government Documents Department