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  • 1. Chourou, S. T.
    et al.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Low-energy dissociative electron attachment to CF22015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 2, article id 022702Article in journal (Refereed)
    Abstract [en]

    We present the results of a theoretical study of dissociative electron attachment (DEA) of low-energy electrons to CF2. We carried out electron scattering calculations using the complex Kohn variational method at the static-exchange and relaxed self-consistent field (SCF) level at the equilibrium geometry and compare our differential cross sections to other results. We then repeated these calculations as a function of the three internal degrees of freedom to obtain the resonance energy surfaces and autoionization widths. We use this data as input to form the Hamiltonian relevant to the nuclear dynamics. The multidimensional wave equation is solved using the multiconfiguration time-dependent Hartree (MCTDH) approach within the local approximation.

  • 2. dos Santos, S. Fonseca
    et al.
    Ngassam, V.
    Orel, A. E.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination of N2H+2016In: Physical Review A, ISSN 2469-9926, Vol. 94, no 2, article id 022702Article in journal (Refereed)
    Abstract [en]

    The direct and indirect mechanisms of dissociative recombination of N2H+ are theoretically studied. At low energies, the electron capture is found to be driven by recombination into bound Rydberg states, while at collision energies above 0.1 eV, the direct capture and dissociation along electronic resonant states becomes important. Electron-scattering calculations using the complex Kohn variational method are performed to obtain the scattering matrix as well as energy positions and autoionization widths of resonant states. Potential-energy surfaces of electronic bound states of N2H and N2H+ are computed using structure calculations with the multireference configuration interaction method. The cross section for the indirect mechanism is calculated using a vibrational frame transformation of the elements of the scattering matrix at energies just above the ionization threshold. Here vibrational excitations of the ionic core from v = 0 to v = 1 and v = 2 for all three normal modes are considered and autoionization is neglected. The cross section for the direct dissociation along electronic resonant states is computed with wave-packet calculations using the multiconfiguration time-dependent Hartree method, where all three internal degrees of freedom are considered. The calculated cross sections are compared to measurements.

  • 3.
    Elander, Nils
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Volkov, Mikhail
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Stenrup, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Mezei, J. Zsolt
    Stockholm University, Faculty of Science, Department of Physics.
    Yarevsky, Evgeny
    Yakolev, Sergey
    Quantum Scattering with the Driven Schrödinger Approachand Complex Scaling2009In: Few-body systems, ISSN 0177-7963, E-ISSN 1432-5411, Vol. 45, no 2-4, p. 197-201Article in journal (Refereed)
    Abstract [en]

    Quantum scattering calculations of two and three-body systems with Coulomb interaction using thedriven Schrödinger equation combined with exterior complex scaling are discussed. A rigorous formulationfor two-body scattering is reported, and its generalization to three-body scattering is considered.

  • 4. Ghassemi, Elham Nour
    et al.
    Larson, Jonas
    Stockholm University, Faculty of Science, Department of Physics. University of Cologne, Germany.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    A diabatic representation of the two lowest electronic states of Li-32014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 15, p. 154304-Article in journal (Refereed)
    Abstract [en]

    Using the Multi-Reference Configuration Interaction method, the adiabatic potential energy surfaces of Li-3 are computed. The two lowest electronic states are bound and exhibit a conical intersection. By fitting the calculated potential energy surfaces to the cubic E circle times epsilon Jahn-Teller model we extract the effective Jahn-Teller parameters corresponding to Li-3. These are used to set up the transformationmatrix which transforms from the adiabatic to a diabatic representation. This diabatization method gives a Hamiltonian for Li-3 which is free from singular non-adiabatic couplings and should be accurate for large internuclear distances, and it thereby allows for bound dynamics in the vicinity of the conical intersection to be explored.

  • 5.
    Hedberg, Hanae Miyano
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nkambule, Sifiso
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Landau-Zener studies of mutual neutralization in collisions of H+ + H- and Be+ + H-2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 22, article id 225206Article in journal (Refereed)
    Abstract [en]

    Semi-classical Landau-Zener studies of mutual neutralization reactions in low-energy H+ + H- and Be+ + H- collisions are performed. Avoided crossings between ionic and covalent states occurring at large internuclear distances are considered, and electronic couplings between these states are estimated using different semi-empirical and ab initio methods and tested on the H+ + H- reaction. The method is then applied to compute the cross sections and final state distributions for mutual neutralization in collisions of H- with Be+. These are reactions that might be important for the modeling of the fusion edge plasma of the divertor of ITER.

  • 6.
    Larson, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universität zu Köln, Germany.
    Ghassemi, Elham Nour
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Anomalous molecular dynamics in the vicinity of a conical intersection2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, no 4, article id 43001Article in journal (Refereed)
    Abstract [en]

    Conical intersections between molecular electronic potential energy surfaces can greatly affect molecular dynamics and chemical properties. Molecular gauge theory is capable of explaining many of these often unexpected phenomena deriving from the physics of the conical intersection. Here we will give an example of anomalous dynamics in the paradigm E x epsilon Jahn-Teller model, which does not allow for a simple explanation in terms of standard molecular gauge theory. By introducing a dual gauge theory, we unwind this surprising behavior by identifying it with an intrinsic spin Hall effect. Thus, this work link knowledge of condensed-matter theories with non-adiabatic molecular dynamics. Furthermore, via ab initio calculations of potential energy surfaces, the findings are as well demonstrated to appear in a realistic system such as the Li-3 molecule.

  • 7.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Fonseca dos Santos, Samantha
    Orel, Ann E.
    Dissociative recombination of HCl+2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 8, article id 084304Article in journal (Refereed)
    Abstract [en]

    The dissociative recombination of HCl+, including both the direct and indirect mechanisms, is studied. For the direct process, the relevant electronic states are calculated ab initio by combining electron scattering calculations to obtain resonance positions and autoionization widths with multi-reference configuration interaction calculations of the ion and Rydberg states. The cross section for the direct dissociation along electronic resonant states is computed by solution of the time-dependent Schrodinger equation. For the indirect process, an upper bound value for the cross section is obtained using a vibrational frame transformation of the elements of the scattering matrix at energies just above the ionization threshold. Vibrational excitations of the ionic core from the ground vibrational state, v = 0, to the first three excited vibrational states, v = 1, v = 2, and v = 3, are considered. Autoionization is neglected and the effect of the spin-orbit splitting of the ionic potential energy upon the indirect dissociative recombination cross section is considered. The calculated cross sections are compared to measurements. Published by AIP Publishing.

  • 8.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nkambule, Sifiso
    Stockholm University, Faculty of Science, Department of Physics.
    Ertan, Emelie
    Stockholm University, Faculty of Science, Department of Physics.
    Söder, Josefine
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann E.
    Studies of HeH: DR, RIP, VE, DE, PI, MN, ...2015In: EPJ Web of Conferences, ISSN 2101-6275, E-ISSN 2100-014X, Vol. 84, article id 03001Article in journal (Refereed)
    Abstract [en]

    The resonant states of HeH are computed by combining structure calculations at a full configuration interaction level with electron scattering calculations carried out using the Complex-Kohn variational method. We obtain the potential energy curves, autoionization widths, as well as non-adiabatic couplings among the resonant states. Using the non-adiabatic couplings, the adiabatic to diabatic transformation matrix can be obtained. A strict diabatization of the resonant states will be used to study various scattering processes where the resonant states are involved. These processes involve high energy dissociative recombination (DR) and ion-pair formation (RIP), resonant and direct dissociative excitation (DE), penning ionization (PI) as well as mutual neutralization (MN).

  • 9.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nkambule, Sifiso M.
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann E.
    Theoretical study of mutual neutralization in He+ + H- collisions2016In: Physical Review A, ISSN 2469-9926, Vol. 94, no 2, article id 022709Article in journal (Refereed)
    Abstract [en]

    Total and differential cross sections for mutual neutralization in He+ and H- collisions at low to intermediate (0.001 eV to 100 eV) are calculated ab initio and fully quantum mechanically. Atomic final-state distributions and isotope effects are investigated. The theoretical model includes dynamics on eleven coupled states of (2)Sigma(+) symmetry, where autoionization is incorporated. The potential-energy curves, autoionization widths, and nonadiabatic couplings of electronic resonant states of HeH are computed by combining structure calculations with electron scattering calculations. The nuclear dynamics is studied using a strict diabatic representation of the resonant states. Effects of rotational couplings between (2)Sigma(+) and (2)Pi electronic states are investigated in the pure precession approximation.

  • 10.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nkambule, Sifiso
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann
    A theoretical study of mutual neutralization of He++H- collisionsManuscript (preprint) (Other academic)
    Abstract [en]

    Total and differential cross sections for mutual neutralization in low energy (0.001 eV -100 eV) He + and H − collisions are calculated ab initio and fully quantum mechanically. Atomic final state distributions and isotope effects are investigated. The theoretical model includes dynamics on eleven coupled states of 2 Σ + symmetry where autoionization is incorporated. The potential energy curves, autoionization widths and non-adiabatic couplings of electronic resonant states of HeH are computed by combining structure calculations with electron scattering calculations. The nuclear dynamics is studied using a strict diabatic representation of the resonant states. Effects of rotational couplings between 2 Σ + and 2 Π electronic states are investigated in the pure precession approximation.

  • 11.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Electronic resonant states of HCO and HOC2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, no 6, p. 62504-Article in journal (Refereed)
    Abstract [en]

    The electronic resonant states of HCO and HOC are calculated using the complex Kohn variational method combined with structure calculations using multireference configuration interaction. No resonant state of HCO crosses the ion potential close to its minimum. Several resonances at higher energies are observed. There are clear indications of avoided crossings between the resonant states. There are resonant states that are repulsive with respect to both radial coordinates, but they remain relatively unchanged in energy as a function of the bending angle. For HOC, there are a manifold of resonant states with similar shapes as the potentials of HCO. However, the resonant states of HOC are lower in energy relative to the ion and could play an important role for dissociative recombination of HOC+ at low collision energies.

  • 12.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Roos, Johanna B.
    Stockholm University, Faculty of Science, Department of Physics.
    Hedberg, Hanae
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann E.
    Reactive collisions involving the BeH molecular system2015In: light element atom, molecule and radical behaviour in the divertor and edge plasma regions, 2015, Vol. 576, article id 012003Conference paper (Refereed)
    Abstract [en]

    In the divertor and fusion edge plasma regions reactive collisions involving the BeH molecular system are taking place. Theoretical ab initio quantum studies of electron collisions with BeH+ resulting in either dissociative recombination, vibrational excitation or dissociative excitation are performed for ions in different vibrational states as well for different isotopologues. Furthermore, the mutual neutralization reaction in collisions of H- with Be+ is studied semiclassically.

  • 13.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stenrup, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann E.
    Stockholm University, Faculty of Science, Department of Physics.
    The role of the direct mechanism in dissociative recombination of HCO+ and HOC+In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622Article in journal (Refereed)
  • 14.
    Larson, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stenrup, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Role of the direct mechanism in dissociative recombination of HCO+ and HOC+2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 4, p. 042702-Article in journal (Refereed)
    Abstract [en]

    Studies of the direct mechanism for dissociative recombination of HCO+ and HOC+ are presented. The calculations involve wave-packet propagation in three dimensions on electronically resonant states of HCO and HOC with the potential-energy surfaces and autoionization widths obtained from ab initio electron scattering and electronic structure calculations. The total cross section and branching ratios for the two molecules and their deuterated isotopologues are calculated and compared to available experiments. The effect of vibrational excitation in DCO+ has been studied as well.

  • 15.
    Linusson, Per
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stenrup, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Andersson, E.
    Heijkenskjold, F.
    Andersson, P.
    Eland, J. H. D.
    Karlsson, L.
    Rubensson, J. -E
    Feifel, R.
    Double photoionization of alcohol molecules2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, no 3, p. 32516-Article in journal (Refereed)
    Abstract [en]

    The double valence photoionization spectra of methanol, ethanol, and n-propyl alcohol have been recorded using a time-of-flight photoelectron-photoelectron coincidence technique. The spectra show a well-defined onset followed by broad rounded bands. The lowest vertical double ionization energies have been determined for all molecules and are found to be 32.1, 29.6, and 28.2 eV, respectively. These energies have been applied along with single ionization energies from conventional photoelectron spectra to investigate a recently derived rule of thumb for determination of the lowest double ionization energy in molecules. Many-electron ab initio calculations have been performed on the dicationic ground states in good agreement with the experimental values. For methanol, also excited dicationic states have been calculated up to about 40 eV and used for a detailed interpretation of the experimental spectrum.

  • 16.
    Mezei, J. Z.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Roos, Johanna Brinne
    Stockholm University, Faculty of Science, Department of Physics.
    Shilyaeva, K.
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Mutual neutralization in low-energy H(+) + F(-) collisions2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 1, p. 012703-Article in journal (Refereed)
    Abstract [en]

    The cross section for mutual neutralization in collisions between H(+) and F(-) ions at low energies ( E <= 10 eV) is calculated using a molecular close-coupling approach. Two different representations of the quasidiabatic potentials and couplings of HF are used. The effect of autoionization on the cross section is investigated. The coupled Schrodinger equation for the nuclear motion is solved using a numerical integration of the corresponding matrix Riccati equation and the cross section for mutual neutralization is computed from the asymptotic value of the logarithmic derivative of the radial wave function. The magnitude of the cross section for mutual neutralization in this reaction is small compared to other systems. This can be understood by the lack of avoided crossings at large internuclear distances. Resonant structures are found in the cross section and these are assigned with dominant angular momentum quantum number. The cross section for mutual neutralization in collisions of D(+) and F(-) ions is also calculated.

  • 17. Mezei, J. Zs
    et al.
    Niyonzima, S.
    Backodissa, D.
    Pop, N.
    Waffeutamo, F. O.
    Chakrabarti, K.
    Motapon, O.
    Wolf, A.
    Robert, J.
    Dulieu, O.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Bultel, A.
    Schneid, I. F.
    Electronic and photonic reactive collisions in edge fusion plasma and interstellar space: application to H-2 and BeH systems2015In: Light element atom, molecule and radical behaviour in the divertor and edge plasma regions, 2015, Vol. 576, article id 012005Conference paper (Refereed)
    Abstract [en]

    Reactive collisional and radiative elementary processes rate coefficients have been either computed using multichannel-quantum-defect theory methods, or measured in merged-beam (storage ring) and crossed-beam experiments. The reaction mechanisms are explained and output data are displayed in ready-to-be-used form, appropriate for the modeling of the kinetics of the edge fusion plasma and of the interstellar molecular clouds.

  • 18.
    Mezei, Zsolt
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Stenrup, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Double charge transfer in low-energy H+ + H- collisions2010In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 1, p. 14701-Article in journal (Refereed)
    Abstract [en]

    The cross section for double charge transfer between H+ and H- at low collision energies (E <= 90 eV) is calculated using a many-state molecular close-coupling model. The wave function is expanded in a diabatic representation of the seven lowest (1)Sigma(+)(g) and the six lowest (1)Sigma(+)(u) states of the hydrogen molecule. The calculated cross section shows clear oscillations as a function of the collision energy, similar to those observed experimentally. However, the magnitude of the calculated cross section is larger than found in experiments. Also, the cross section for double charge transfer in collisions between D+ and H- is calculated.

  • 19. Motapon, O.
    et al.
    Niyonzima, S.
    Chakrabarti, K.
    Mezei, J. Zs.
    Backodissa, D.
    Ilie, S.
    Epee, M. D. Epee
    Peres, B.
    Lanza, M.
    Tchakoua, T.
    Pop, N.
    Argoubi, F.
    Telmini, M.
    Dulieu, O.
    Bultel, A.
    Robert, J.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Schneider, I. F.
    Advances in the MQDT approach of electron/molecular cation reactive collisions: High precision extensive calculations for applications2015In: DR2013: Ninth international conference on dissociative recombination: theory, experiment, and applications, 2015, Vol. 84, article id 02003Conference paper (Refereed)
    Abstract [en]

    Recent advances in the stepwise multichannel quantum defect theory approach of electron/molecular cation reactive collisions have been applied to perform computations of cross sections and rate coefficients for dissociative recombination and electron-impact rovibrational transitions of H-2(+), BeH+ and their deuterated isotopomers. At very low energy, rovibronic interactions play a significant role in the dynamics, whereas at high energy, the dissociative excitation strongly competes with all other reactive processes.

  • 20. Niyonzima, S.
    et al.
    Ilie, S.
    Pop, N.
    Mezei, J. Zs.
    Chakrabarti, K.
    Morel, V.
    Peres, B.
    Little, D. A.
    Hassouni, K.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Benredjem, D.
    Bultel, A.
    Tennyson, J.
    Reiter, D.
    Schneider, I. F.
    Low-energy collisions between electrons and BeH+: Cross sections and rate coefficients for all the vibrational states of the ion2017In: Atomic Data and Nuclear Data Tables, ISSN 0092-640X, E-ISSN 1090-2090, Vol. 115, p. 287-308Article in journal (Refereed)
    Abstract [en]

    We provide cross sections and Maxwell rate coefficients for reactive collisions of slow electrons with BeH+ ions on all the eighteen vibrational levels (X-1 Sigma(+), v(i)(+) = 0, 1, 2, ... , 17) using a Multichannel Quantum Defect Theory (MQDT)-type approach. These data on dissociative recombination, vibrational excitation and vibrational de-excitation are relevant for magnetic confinement fusion edge plasma modeling and spectroscopy, in devices with beryllium based main chamber materials, such as the International Thermonuclear Experimental Reactor (ITER) and the Joint European Torus (JET). Our results are presented in graphical form and as fitted analytical functions, the parameters of which are organized in tables.

  • 21. Niyonzima, S.
    et al.
    Lique, F.
    Chakrabarti, K.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Schneider, I. F.
    Multichannel-quantum-defect-theory treatment of reactive collisions between electrons and BeH+2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 2, p. 022713-Article in journal (Refereed)
    Abstract [en]

    A theoretical treatment of dissociative recombination (DR), vibrational excitation, and vibrational deexcitation of the BeH+ ion in its four lowest vibrational states (X (1)Sigma(+), v(i)(+) = 0,1,2,3) is reported. The multichannel quantum defect theory is used to determine cross sections and rate coefficients. Three electronic symmetries of BeH ((2)Pi, (2)Sigma(+), and (2)Delta) have been included in the calculations. At low energies the DR is dominated by capture into states of (2)Pi symmetry. Satisfactory agreement with results obtained using the wave packet approach is reached at intermediate energies despite significant differences at low energies. Cross sections and rate coefficients suitable for the modeling of the kinetics of BeH+ in fusion plasmas and in the stellar atmospheres are presented and discussed. DOI: 10.1103/PhysRevA.87.022713

  • 22. Niyonzima, S.
    et al.
    Pop, N.
    Iacob, F.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, A. E.
    Mezei, J. Zs
    Chakrabarti, K.
    Laporta, V.
    Hassouni, K.
    Benredjem, D.
    Bultel, A.
    Tennyson, J.
    Reiter, D.
    Schneider, I. F.
    Low-energy collisions between electrons and BeD+2018In: Plasma sources science & technology (Print), ISSN 0963-0252, E-ISSN 1361-6595, Vol. 27, no 2, article id 025015Article in journal (Refereed)
    Abstract [en]

    Multichannel quantum defect theory is applied in the treatment of the dissociative recombination and vibrational excitation processes for the BeD+ ion in the 24 vibrational levels of its ground electronic state (X (1)Sigma(+), v(i)(+) = 0 ... 23). Three electronic symmetries of BeD** states ((2)Pi, (2)Sigma(+), and (2)Delta) are considered in the calculation of cross sections and the corresponding rate coefficients. The incident electron energy range is 10(-5)-2.7 eV and the electron temperature range is 100-5000 K. The vibrational dependence of these collisional processes is highlighted. The resulting data are useful in magnetic confinement fusion edge plasma modeling and spectroscopy, in devices with beryllium based main chamber materials, such as ITER and JET, and operating with the deuterium-tritium fuel mix. An extensive rate coefficients database is presented in graphical form and also by analytic fit functions whose parameters are tabulated in the supplementary material.

  • 23.
    Nkambule, Sifiso M.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Lecointre, Julien
    Urbain, Xavier
    Differential and total cross sections of mutual neutralization in low-energy collisions of isotopes of H+ + H-2016In: Physical Review A, ISSN 2469-9926, Vol. 93, no 3, article id 032701Article in journal (Refereed)
    Abstract [en]

    Mutual neutralization in the collisions of H+ and H- is studied both theoretically and experimentally. The quantum-mechanical ab initio model includes covalent states associated with the H(1)+H(n <= 3) limits and the collision energy ranges from 1 meV to 100 eV. The reaction is theoretically studied for collisions between different isotopes of the hydrogen ions. From the partial wave scattering amplitude, the differential and total cross sections are computed. The differential cross section is analyzed in terms of forward- and backward-scattering events, showing a dominance of backward scattering which can be understood by examining the phase of the scattering amplitudes for the gerade and ungerade set of states. The isotope dependence of the total cross section is compared with the one obtained using a semiclassical multistate Landau-Zener model. The final state distribution analysis emphasizes the dominance of the n = 3 channel for collisions below 10 eV, while at higher collision energies, the n = 2 channel starts to become important. For collisions of ions forming a molecular system with a larger reduced mass, the n = 2 channel starts to dominate at lower energies. Using a merged ion-beam apparatus, the branching ratios for mutual neutralization in H+ and H- collisions in the energy range from 11 to 185 eV are measured with position- and time-sensitive particle detectors. The measured and calculated branching ratios satisfactorily agree with respect to state contributions.

  • 24.
    Nkambule, Sifiso M.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    dos Santos, Samantha Fonseca
    Orel, Ann E.
    Theoretical study of the mechanism of H2O+ dissociative recombination2015In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 92, no 1, article id 012708Article in journal (Refereed)
    Abstract [en]

    By combining electronic structure and scattering calculations, quasidiabatic potential energy surfaces of both bound Rydberg and electronic resonant states of the water molecule are calculated at the multireference configuration-interaction level. The scattering matrix calculated at low collision energy is used to obtain explicitly all couplings elements responsible for the electronic capture to bound Rydberg states. These are used to estimate the cross section arising from the indirect mechanism of dissociative recombination. Additionally, the role of the direct capture and dissociation through the resonant states is explored using wave-packet propagation along one-dimensional slices of the multidimensional potential energy surfaces.

  • 25.
    Nkambule, Sifiso M.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nurzia, Pietro
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Mutual neutralization in collisions of Li+ and F-2015In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 462, p. 23-27Article in journal (Refereed)
    Abstract [en]

    Mutual neutralization in collisions of Li+ and F is driven by an avoided crossing between the two lowest (1)Sigma(+) electronic states of the LiF system. These electronic states are computed using the multi-reference configuration interaction method. We investigate how the adiabatic potential energy curves and the non-adiabatic coupling element depend on the choice of the reference configurations as well as the basis set. Using diabatic states, the total and differential cross sections for mutual neutralization are computed.

  • 26.
    Stenrup, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    A computational study of radiationless deactivation mechanisms of furan2011In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 379, no 1-3, p. 6-12Article in journal (Refereed)
    Abstract [en]

    Possible mechanisms for the radiationless deactivation of photo-excited furan have been investigated using high-level electronic structure methods. Two different conical intersections between the S0 and S1 electronic states have been characterized, both involving various degrees of CO bond cleavage. One of these corresponds to a planar ring-opened structure and the other to an asymmetric ring-puckered structure. Calculations have been performed in order to establish the vertical electronic spectrum and to investigate the behaviour of the potential energy surfaces as the intersections are approached. The present results indicate that both crossings can be accessed through exothermic and barrierless processes after vertical excitation into the optically bright S2(ππ∗) state. These features make them good candidates to account for efficient radiationless deactivation in furan. The deactivation pathways considered in the present work are close analogues of those previously described for other five-membered heterocycles.

  • 27.
    Stenrup, Michael
    et al.
    Kungliga tekniska högskolan (KTH), Skolan för bioteknologi, Teoretisk kemi.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Mutual neutralization in low-energy H+ + H- collisions: A quantum ab initio study2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 79, no 1, p. 012713-Article in journal (Refereed)
    Abstract [en]

    The mutual neutralization of H+ and H at low collision energies is studied by means of a molecular close-coupling approach. All degrees of freedom are treated at the full quantum level also taking into account the identity of the nuclei. The relevant 1Σg+ and 1Σu+ electronic states as well as the associated nonadiabatic radial couplings are calculated for internuclear distances between 0.5 and 50a0. Following a transformation into a strictly diabatic basis, these quantities enter into a set of coupled equations for the motion of the nuclei. Numerical solution of these equations allows the cross sections for neutralization into the H(1)+H(n), n=1,2,3 final states to be calculated. In the present paper, results are reported for the collision energy region 0.001–100 eV, with special emphasis on the important energy region below 10 eV. The low temperature rate coefficient is obtained from a parametrization of the calculated cross section and is estimated to be valid over the range 10–10 000 K.

  • 28.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Karlsson, Hans O.
    Larson, Jonas
    Quantum interference structures in trapped ion dynamics beyond the Lamb-Dicke and rotating wave approximations2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 77, no 5Article in journal (Refereed)
    Abstract [en]

    We apply wave-packet methods to study an ion-trap system imposing neither the rotating wave nor the Lamb-Dicke approximations. By this approach we show the existence of states with restricted phase-space evolution as a genuine consequence of quantum interference between wave-packet fractions. A particular instance of such a state oscillates between maximal entanglement and pure disentanglement between the constitute subsystems, where the characteristic crossover time is very rapid. Over longer time periods the dynamics of these states exhibits collapse-revival patterns with well-resolved fractional revivals in autocorrelation, inversion, and entanglement.

  • 29.
    Wang, Dong
    et al.
    Stockholm University, Faculty of Science.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Hansson, Tony
    Stockholm University, Faculty of Science, Department of Physics.
    Karlsson, Hans O.
    Molecular quantum wave-packet splitting and revivals in shared phase space2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 79, no 2, p. 23402-Article in journal (Refereed)
    Abstract [en]

    The evolution of a molecular wave packet created by an ultrashort laser pulse in a system of two coupled bound states is investigated by quantum dynamics calculations and semiclassical theory. Under suitable dynamical quantum interference conditions, the wave packet may be split into two separable fractions that move in different but partially overlapping regions of the energetically available phase space. Each wave-packet part can be individually addressed in the divided parts of the molecular phase space, and they are shown to go through separate long-term collapse-revival cycles analogous to those of wave packets moving in single anharmonic potentials. In a pump-probe scheme, the dynamics of the system would look very different depending on what internuclear distances are probed. The regular dynamics observable in the separated parts of the phase space takes on a quite irregular appearance in the regions that are shared by the wave-packet components. The wave-packet regularity is shown to depend sensitively on the pump pulse wavelength, which is a reflection of the energy range over which the quantum interference conditions are maintained. These conditions, as well as the wave-packet fraction revival times, are well reproduced by semiclassical theory.

  • 30. Yarevsky, E.
    et al.
    Yakovlev, S. L.
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Elander, Nils
    Stockholm University, Faculty of Science, Department of Physics.
    Potential-splitting approach applied to the Temkin-Poet model for electron scattering off the hydrogen atom and the helium ion2015In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 11Article in journal (Refereed)
    Abstract [en]

    The study of scattering processes in few body systems is a difficult problem especially if long range interactions are involved. In order to solve such problems, we develop here a potential-splitting approach for three-body systems. This approach is based on splitting the reaction potential into a finite range core part and a long range tail part. The solution to the Schrodinger equation for the long range tail Hamiltonian is found analytically, and used as an incoming wave in the three body scattering problem. This reformulation of the scattering problem makes it suitable for treatment by the exterior complex scaling technique in the sense that the problem after the complex dilation is reduced to a boundary value problem with zero boundary conditions. We illustrate the method with calculations on the electron scattering off the hydrogen atom and the positive helium ion in the frame of the Temkin-Poet model.

  • 31.
    Zhang, Mingwu
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Cai, Xiaohong
    Larson, Åsa
    Stockholm University, Faculty of Science, Department of Physics.
    Orel, Ann E.
    Theoretical study of dissociative recombination of Cl(2)(+)2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 5, p. 052707-Article in journal (Refereed)
    Abstract [en]

    Theoretical studies of low-energy electron collisions with Cl(2)(+) leading to direct dissociative recombination are presented. The relevant potential energy curves and autoionization widths are calculated by combining electron scattering calculations using the complex Kohn variational method with multireference configuration interaction structure calculations. The dynamics on the four lowest resonant states of all symmetries is studied by the solution of a driven Schrodinger equation. The thermal rate coefficient for dissociative recombination of Cl(2)(+) is calculated and the influence on the thermal rate coefficient from vibrational excited target ions is investigated.

1 - 31 of 31
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