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Double Photoionization of Aligned Molecular Hydrogen

Description: We present converged, completely ab initio calculations ofthe triple differential cross sections for double photoionization ofaligned H2 molecules for a photon energy of 75.0 eV. The method ofexterior complex scaling, implemented with both the discrete variablerepresentation and B-splines, is used to solve the Schroedinger equationfor a correlated continuum wave function corresponding to a single photonhaving been absorbed by a correlated initial state. Results for a fixedinternuclear distance are compared with recent experiments and show thatintegration over experimental angular and energy resolutions is necessaryto produce good qualitative agreement, but does not eliminate somediscrepancies. Limitations of current experimental resolution are shownto sometimes obscure interesting details of the crosssection.
Date: July 21, 2006
Creator: Vanroose, Wim; Horner, Daniel A.; Martin, Fernando; Rescigno,Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

Resonant electron-CF collision processes

Description: Electronic structure methods are combined with variationalfixed-nuclei electron scattering calculations and nuclear dynamicsstudies to characterize resonant vibrational excitation and electronattachment processes in collisions between low-energy electrons and CFradicals. Several low-lying negative ion states are found which give riseto strong vibrational excitation and which are expected to dominate thelow-energy electron scattering cross sections. We have also studiedseveral processes which could lead to production of negative ions (F- andC-), However, in contrast to other recent predictions, we do not find CFin itsground state to be a significant source of negative ion productionwhen interacting with thermal electrons.
Date: March 18, 2005
Creator: Trevisan, Cynthia S.; Orel, Ann E. & Rescigno, Thomas N.
Partner: UNT Libraries Government Documents Department

Elastic Scattering of Low-Energy Electrons byTetrahydrofuran

Description: We present the results of ab initio calculations for elasticelectron scattering by tetrahydrofuran (THF) using the complex Kohnvariational method. We carried out fixed-nuclei calculations at theequilibrium geometry of the target molecule for incident electronenergies up to 20 eV. The calculated momentum transfer cross sectionsclearly reveal the presence of broad shape resonance behavior in the 8-10eV energy range, in agreement with recent experiments. The calculateddifferential cross sections at 20 eV, which include the effects of thelong-range electron-dipole interaction, are alsofound to be in agreementwith the most recent experimental findings.
Date: May 9, 2006
Creator: Trevisan, Cynthia S.; Orel, Ann E. & Rescigno, Thomas N.
Partner: UNT Libraries Government Documents Department

Single and Triple Differential Cross Sections for DoublePhotoionization of H-

Description: The hydride anion H- would not be bound in the absence ofelectron correlation. Electron correlation drives the doublephotoionization process and, thus should impact double photoionizationresults most strongly for H-. We present fully differential crosssections for the three-body breakup of H- by single photon absorption.The absolute triple-differential and single-differential cross sectionswere yielded by ab initio calculations making use of exterior complexscaling within a discrete variable representation partialwave basis.Results calculated at photon energies of 18eV and 30eV are compared withreported cross sections for helium calculated at 20eV above the doubleionization threshold. These comparisons show a clear signature of initialstate correlation that differentiate the He and H- cases.
Date: February 15, 2007
Creator: Yip, Frank L.; Horner, Daniel A.; McCurdy, C. William & Rescigno,Thomas N.
Partner: UNT Libraries Government Documents Department

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

ENERGY DERIVATIVES FOR CONFIGURATION INTERACTION WAVEFUNCTIONS

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

ON RAINBOW SCATTERING IN INELASTIC MOLECULAR COLLISIONS

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

2012 VIBRATIONAL SPECTROSCOPY GORDON RESEARCH CONFERENCE, AUGUST 5-10, 2012

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

ROTATIONAL EXCITATION OF CO BY He IMPACT

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

SYSTEMATICS OF TARGET AND PROJECTILE K X-RAY PRODUCTION AND REC FOR 20-80 MeV Cl{sup q+} ION INCIDENT ON 25-200{micro}g/cm{sup 2} Cu TARGETS

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

COLLISIONS OF FAST, HIGHLY STRIPPED CARBON, NIOBIUM, AND LEAD IONS WITH MOLECULAR HYDROGEN

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

EVOLUTION OF PROJECTILE DOUBLE K VACANCY FRACTIONS WITH TARGET THICKNESS IN ION-ATOM COLLISIONS

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

IONIZATION OF RARE-GAS TARGETS BY COLLISIONS OF FAST HIGHLY CHARGED PROJECTILES

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

Ro-vibrational Relaxation Dynamics of PbF Molecules

Description: In 1950 Purcell and Ramsey suggested that the electron might have a CP-violating electric dipole moment (e-EDM) proportional to its spin angular momentum. This possibility initiated an ongoing hunt for the e-EDM that has been spurred on by the recognition of the importance of CP-violation to the formation of a matter-dominated universe[2] as well as a difference in magnitude of the Supersymmetric and Standard Model[4] prediction for its value. The current limit on the e-EDM is 1.6E−27 e·cm as determined in a Ramsey beam resonance study of the Tl atom. The PbF molecule provides a unique opportunity to measure the e-EDM. The molecule’s odd electron, heavy mass, and large internal field combine to give it an intrinsic sensitivity to an e-EDM that is over three orders of magnitude bigger than that of the Tl atom. In addition to this increased intrinsic sensitivity, the ground state of the PbF molecule allows for a "magic" electric field at which the magnetic moment vanishes[7]. All of these advantages create an opportunity to significantly lower the current limit on the e-EDM. These advantages can only be realized if an intense source of ground-state PbF molecules can be created and detected with high efficiency. The scope of this project is to (1) create a rotationally cold molecular beam source of PbF, (2) achieve a continuous ionization scheme for sensitive state selective detection of the PbF molecule.
Date: April 8, 2011
Creator: Shafer-Ray, Neil
Partner: UNT Libraries Government Documents Department