F. A. Gianturco

One-electron resonances in electron scattering from polyatomic molecules

Abstract One-electron resonances in electron scattering from polyatomic molecules were examined using set of interconnected models. We compared resonant states predicted from the virtual orbitals of a minimum-basis-set self-consistent-field (MBS-SCF) calculation with scattering resonances found using both a purely local model potential for the electron-molecule interaction based on an adiabatic separation of the angular and radial motion and a more accurate exact-static-exchange-plus-model-correlation—polarization interaction potential. Considering electron scattering from N2, SF6, and C6H6, we found that the MBS-SCF virtual orbitals were an excellent predictor of the symmetry and approximate location of one-electron resonances. The adiabatic radical potentials were very useful in understanding the mechanism for resonant trapping, although strong non-adiabatic coupling sometimes required more than one adiabatic potential to be considered to accurately represent the resonant dynamics. The essential feature...

Anomalous vibrational excitation of O2 in collisions with protons at 10 eV when compared with N2, CO and NO

Structured time-of-flight spectra of protons scattered from O2 have been measured at scattering angles 5 degrees <or= nu cm<or=21 degrees at Ecm=9.5 eV. A comparison with similar measurements for N2, CO and NO reveals a factor of three greater vibrational energy transfer and roughly a factor of two less rotational energy transfer. On the basis of molecular orbitals an explanation involving a charge transfer mechanism is presented for the enhancement of vibrational excitation in O2.

One-electron resonances and computed cross sections in electron scattering from the benzene molecule

One-electron resonances arising in electron scattering processes from a nonlinear polyatomic target, the benzene molecule, have been examined using various related methods. First, we have carried out calculations over a broad range of collision energies (from about 0.001 eV up to about 30 eV) by solving the scattering equations which use a parameter-free exact-static-exchangeplus-correlation-polarization potential to treat the electron–molecule interaction in all scattering symmetries. The entire range of features produced by the calculations was then related to specific structural properties of the scattering functions which give rise to the resonances. This analysis was done by using wave functions obtained with a local model potential approximation to the full potential used in the scattering calculations. These scattering functions were also related to the virtual orbitals obtained from a minimum basis set self-consistent field calculation. Additionally, for each resonant state found in this study we ...

One-particle resonances in low-energy electron scattering from C60

The quantum dynamics of low-energy electron scattering from C60 molecules is carried out using the full anisotropic interaction between the molecule at its equilibrium geometry and the impinging electron. The interaction is constructed using a nonempirical model potential for the short-range dynamical correlation between the scattered electron and the bound electrons, while both the static interaction and the nonlocal exchange interaction are treated correctly. The fairly large size of the carbon cage, and the hollow structure which is created inside it, are unique features of the C60 molecule that are shown here to play a very important role in forming a broad variety of metastable electron-attachment states without electronic excitation being involved. In spite of various aspects of the resonant process which are not considered in the present treatment, the calculations show very clearly the occurrence of several trapping processes for the scattered electrons which could be amenable to experimental obse...

The H2–Ne interaction

New measurements of the elastic and rotationally inelastic differential cross sections for the Ne–D2, Ne–H2 system are compared with exact and approximate quantum calculations. The three most recent high quality, semiempirical interaction potentials available in the literature for the Ne–H2 system yield consistent theoretical scattering cross sections for Ne–H2 and for Ne–D2. They also agree with previous and with present inelastic cross section measurements for D2. However, the theory underestimates by 30% the newly measured rotational excitation in Ne–H2 collisions discussed here. We therefore propose a new potential with a modified repulsive barrier that succeeds in describing both Ne–D2 and Ne–H2 rotationally inelastic scattering experiments for j=0→j’=2 within an accuracy of a few percent.

On the scattering of low‐energy electrons by sulphur hexafluoride

The collision between a beam of electrons and gaseous molecules of sulphur hexafluoride (SF6) are studied from a theoretical and computational point of view, by solving the multichannel scattering problem within the close‐coupling (CC) approach that uses a symmetry‐adapted, single‐center‐expanded (SCE) description of the continuum functions. The static and exchange interactions are treated exactly within the basis set expansion and correlation forces are introduced in local form using a density functional model (FEG) without empirical parameters. Elastic observables (rotationally summed) are obtained over a broad range of energies, both for the integral and differential cross sections, and compared with the existing experiments. The symmetry and nature of the observed resonances are analyzed and discussed. One finds, in general, very satisfactory accord between the present calculations and the measured cross sections.

Potential energy curves for the (ArH)+ and (NeH)+ systems from the interplay of theory and experiments

The ground state potential energy curves for protons interacting with Ar and Ne atoms are determined by the analysis of new, highly accurate measurements of the elastic differential cross sections at a laboratory collision energy of 14.8 eV. Accompanying theoretical results from SCF-CI calculations are used as starting points to generate analytic potentials that are able to fit all available experimental cross sections for both systems. The final results provide the full shape of the potential curves and give the best existing fit to the measured cross sections for elastic scattering at several energies from 2eV to 30eV.

Electron scattering from gaseous SF6: Comparing calculations with experiments

The dynamical observables associated with low-energy electron scattering from SF6 molecules in the gas-phase, e.g., elastic differential cross sections, integral elastic cross sections and momentum transfer cross sections, are computed using quantum methods and describing the full interaction between the molecule and the impinging electron without empirical parameters. The above quantities are obtained over an energy interval ranging from a few meV up to 100 eV and the results are compared with the available experiments. Various aspects of the theoretical method employed are analyzed in relation to their agreement with the experimental data discussed in this work.

A semiclassical model for polarization forces in collisions of electrons and positrons with helium atoms

Abbsbact. A simple semiclassical model is proposed for the calculation of the polarization potential at short range whae the impacting electron penetrates the electron cloud of the target atom. The new method is applied to the scattering of electrons and positrons from He atoms at energies between 0.1 and 50 eV. The model is described in detail and is shown to produce a local effective potential which is computationally wry easy to devise. Calculations for electron scattering are carried out for the elastic integral cross sections and for angular distributions of electrons at several collision energies and compared both with experiments and with more sophisticated calculations. The agreement of the presmt results with experiments is invariably very good. Further test calculations for the positron scattering processes also agree very well with the available experiments and with other theoretid predictions.

Some properties of the lower electronic states for nonlinear He3+ clusters

Accurate, highly correlated calculations have been carried out for the ground electronic state and for a few of the lower excited electronic states, two of which are discussed in this work, of the trimer ionic helium cluster. Both linear asymmetric and nonlinear, symmetric, and asymmetric, configurations have been considered over a rather broad range of nuclear geometries. The results confirm the experimentally found [Chem. Phys. 102, 2773 (1995)] fragmentation patterns involving He and He+ fragments only and further suggest a range of possible nuclear geometries from which nonadiabatic couplings could also lead to He2+ fragments, albeit with a lower probability than the former channels.