Local Complex Potential Model Research Articles

Quantum dynamics study on the binding of a positron to vibrationally excited states of hydrogen cyanide molecule

We present computational results of vibrationally enhanced positron annihilation in the e++HCN/DCN collisions within a local complex potential model. Vibrationally elastic and inelastic cross sections and effective annihilation rates were calculated by solving a time-dependent complex-potential Schrödinger equation under the ab initio potential energy surface for the positron attached HCN molecule, [HCN; e+], with multi-component configuration interaction level (Kita and Tachikawa, 2014). We discuss the effect of vibrational excitation on the positron affinities from the obtained vibrational resonance features.

Theoretical resonant electron-impact vibrational excitation, dissociative recombination and dissociative excitation cross sections of ro-vibrationally excited BeH+ ion

A theoretical study of resonant vibrational excitation, dissociative recombination and dissociative excitation processes of the beryllium monohydride cation, BeH+, induced by electron impact, is reported. Full sets of ro-vibrationally-resolved cross sections and of the corresponding Maxwellian rate coefficients are presented for the three processes. Particular emphasis is given to the high-energy behaviour. Potential curves of , and symmetries and the corresponding resonance widths, obtained from R-matrix calculations, provide the input for calculations which use a local complex-potential model for resonant collisions in each of the three symmetries. Rotational motion of nuclei and isotopic effects are also discussed. The relevant results are compared with those obtained using a multichannel quantum defect theory method. Full results are available from the Phys4Entry database.

Calculated low-energy electron-impact vibrational excitation cross sections for CO2 molecule

Vibrational-excitation cross sections of ground electronic states of a carbon dioxide molecule by electron-impact through CO shape resonance is considered in the separation of the normal modes approximation. Resonance curves and widths are computed for each vibrational mode. The calculations assume a decoupling between normal modes and employ the local complex potential model for the treatment of nuclear dynamics, usually adopted for electron-scattering involving diatomic molecules. Results are presented for excitation up to 10 vibrational levels in each mode and a comparison with data present in the literature is discussed.

Theoretical vibrational-excitation cross sections and rate coefficients for electron-impact resonant collisions involving rovibrationally excited N2 and NO molecules

Electron-impact vibrational-excitation cross sections, involving rovibrationally excited N2 and NO molecules, are calculated for collisions occurring through the nitrogen resonant electronic state , and the three resonant states of nitric oxide NO−(3Σ−, 1Δ, 1Σ+). Complete sets of cross sections have been obtained for all possible transitions involving 68 vibrational levels of and 55 levels of NO(X 2Π), for incident electron energy between 0.1 and 10 eV. In order to study the rotational motion in the resonant processes, cross sections have also been computed for rotationally elastic transitions characterized by the rotational quantum number J running from 0 to 150. The calculations are performed within the framework of the local complex potential model, using potential energies and widths optimized to reproduce the experimental cross sections available in the literature. Rate coefficients are calculated for transitions between all vibrational levels by assuming a Maxwellian electron energy distribution function in the temperature range from 0.1 to 100 eV.All numerical data are available at http://users.ba.cnr.it/imip/cscpal38/phys4entry/database.html

Cross sections for 14-eVe-H2resonant collisions: Isotope effect in dissociative electron attachment

The process of dissociative attachment of electrons to molecular hydrogen and its isotopes in the energy range at approximately 14 eV is investigated. The dissociative electron attachment cross sections for all six hydrogen isotopes are calculated over an extended range of electron energies using the local complex potential model with the excited Rydberg {sup 2}{Sigma}{sub g}{sup +} electronic state of H{sub 2}{sup -} acting as the intermediate resonant state. A significant isotope effect in theoretical electron attachment cross sections is observed, in agreement with previous predictions and experimental observations. A two-parameter analytic expression for the cross section is derived from the theory that fits accurately the numerically calculated cross sections for all isotopes. Similarly, an analytic mass-scaling relation is derived from the theory that accurately reproduces the numerically calculated rate coefficients for all isotopes in the 0.1-1000 eV temperature range by using the rate coefficient for the H{sub 2} isotope only. The latter is represented by an analytic fit expression with two parameters only.

Three-body breakup in dissociative electron attachment to the water molecule

We report the results of ab initio calculations on dissociative electron attachment to water that demonstrate the importance of including three-body breakup in the dissociation dynamics. While three-body breakup is ubiquitous in the analogous process of dissociative recombination, its importance in low-energy dissociative electron attachment to a polyatomic target has not previously been quantified. Our calculations indicate that three-body breakup is a major component of the observed ${\mathrm{O}}^{\ensuremath{-}}$ cross section. Our studies suggest that the local complex potential model provides a generally accurate picture of the experimentally observed features in this polyatomic system.

Dissociative electron attachment to acetylene

The mechanism and cross section for dissociative electron attachment of acetylene after collision with electrons in the 0--7 eV range is reported. The positions of the resonances and the autoionization widths are determined by electron scattering calculations using the complex Kohn variational method. The complex potential energy surface relevant to the metastable negative ion ${\text{C}}_{2}{\text{H}}_{2}^{\ensuremath{-}\ensuremath{\ast}}$ is constructed as a function of the $\text{C}\ensuremath{\equiv}\text{C}$ and C--H stretches and the CCH angle. The lowest resonant potential is then used as input for the study of the dissociation dynamics within the local complex potential model using the multiconfiguration time-dependent Hartree method. The calculated dissociative electron attachment cross section as a function of electron energy is compared to available experimental findings.

Erratum: “Dissociative electron attachment to theH2Omolecule. II. Nuclear dynamics on coupled electronic surfaces within the local complex potential model” [Phys. Rev. A75, 012711 (2007)

Erratum: “Dissociative electron attachment to the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>molecule. II. Nuclear dynamics on coupled electronic surfaces within the local complex potential model” [Phys. Rev. A<b>75</b>, 012711 (2007)

Dissociative electron attachment to theH2Omolecule. II. Nuclear dynamics on coupled electronic surfaces within the local complex potential model

We report the results of a first-principles study of dissociative electron attachment to ${\mathrm{H}}_{2}\mathrm{O}$. The cross sections were obtained from nuclear dynamics calculations carried out in full dimensionality within the local complex potential model by using the multiconfiguration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential-energy surfaces for the three ($^{2}B_{1}$, $^{2}A_{1}$, and $^{2}B_{2}$) electronic Feshbach resonances involved in this process. These three metastable states of ${\mathrm{H}}_{2}{\mathrm{O}}^{\ensuremath{-}}$ undergo several degeneracies, and we incorporate both the Renner-Teller coupling between the $^{2}B_{1}$ and $^{2}A_{1}$ states as well as the conical intersection between the $^{2}A_{1}$ and $^{2}B_{2}$ states into our treatment. The nuclear dynamics are inherently multidimensional and involve branching between different final product arrangements as well as extensive excitation of the diatomic fragment. Our results successfully mirror the qualitative features of the major fragment channels observed, but are less successful in reproducing the available results for some of the minor channels. We comment on the applicability of the local complex potential model to such a complicated resonant system.

Angular dependence of dissociative electron attachment to polyatomic molecules: Application to theB12metastable state of theH2OandH2Sanions

The angular dependence of dissociative electron attachment (DEA) to polyatomic targets is formulated in the local complex potential model, under the assumption that the axial recoil approximation describes the dissociation dynamics. An additional approximation, which is found to be valid in the case of ${\mathrm{H}}_{2}\mathrm{O}$ but not in the case of ${\mathrm{H}}_{2}\mathrm{S}$, makes it possible to describe the angular dependence of DEA solely from an analysis of the fixed-nuclei entrance amplitude, without carrying out nuclear dynamics calculations. For ${\mathrm{H}}_{2}\mathrm{S}$, the final-vibrational-state-specific angular dependence of DEA is obtained by incorporating the variation of the angular dependence of the entrance amplitude with nuclear geometry into the nuclear dynamics. Scattering calculations using the complex Kohn method and, for ${\mathrm{H}}_{2}\mathrm{S}$, full quantum calculations of the nuclear dynamics using the multiconfiguration time-dependent Hartree method, are performed.

Nonlocal model of dissociative electron attachment and vibrational excitation of NO

We present the results of a study of elastic scattering and vibrational excitation of NO by electron impact in the low-energy $(0--2\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ region where the cross sections are dominated by resonance contributions. The $^{3}\ensuremath{\Sigma}^{\ensuremath{-}}$, $^{1}\ensuremath{\Delta}$, and $^{1}\ensuremath{\Sigma}^{+}$ $\mathrm{N}{\mathrm{O}}^{\ensuremath{-}}$ resonance lifetimes are taken from our earlier study [Phys. Rev. A 69, 062711 (2004)], but the resonance energies used here are obtained from different configuration-interaction studies. Here we employ a more elaborate nonlocal treatment of the nuclear dynamics, which is found to remedy the principal deficiencies of the local complex potential model we employed in our earlier study, and gives cross sections in better agreement with the most recent experiments. We also present cross sections for dissociative electron attachment to NO leading to ground-state products, ${\mathrm{O}}^{\ensuremath{-}}(^{2}\mathrm{P})+\mathrm{N}(^{4}\mathrm{S})$. The calculations show that, while the peak cross sections starting from NO in its ground vibrational state are very small $(\ensuremath{\sim}{10}^{\ensuremath{-}20}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2})$, the cross sections are extremely sensitive to vibrational excitation of the target and should be readily observable for target NO molecules excited to $\ensuremath{\nu}=10$ and above.

Dynamics of dissociative attachment of electrons to water through theB12metastable state of the anion

Calculations of cross sections for dissociative attachment to water through the $^{2}B_{1}$ resonance state are presented using the ab initio surfaces calculated previously for the energy ${E}_{R}$ and width $\ensuremath{\Gamma}$ of this resonance state as a function of nuclear geometry. The dynamics of the dissociative attachment process are treated in full dimensionality using the local complex potential model. For the ${\mathrm{H}}^{\ensuremath{-}}+\mathrm{OH}$ channel, the calculations presented here are in substantial agreement with experiment with regard to total cross section and vibrational excitation of the $\mathrm{OH}$ fragment. Cross sections for dissociative attachment to excited initial ro-vibrational states are presented and isotope effects are also examined.

Low-energy electron scattering ofNO:Ab initioanalysis of theΣ−3,Δ1, andΣ+1shape resonances in the local complex potential model

We present an ab initio study of elastic scattering and vibrational excitation of $\mathrm{NO}$ by low-energy $(0--2.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ electron impact. The low-energy scattering cross sections are dominated by shape resonance contributions associated with the $^{3}\ensuremath{\Sigma}^{\ensuremath{-}}$, $^{1}\ensuremath{\Delta}$, and $^{1}\ensuremath{\Sigma}^{+}$ states of ${\mathrm{NO}}^{\ensuremath{-}}$. Resonance parameters for the three anion states were extracted from an analysis of fixed-nuclei variational (complex Kohn) calculations that employed elaborate trial wave functions. Independent estimates of the resonance parameters were obtained by analytically continuing the results of large-scale coupled-cluster calculations into the plane of complex momentum. The local complex potential model was used to calculate vibrational excitation cross sections, as well as the resonant portion of the vibrationally elastic cross sections. These results were combined with background contributions from the fixed-nuclei calculations to compute elastic and grand total cross sections. Our results capture the essential features of recent measurements of the cross sections, but suggest the need at lower energies for a more sophisticated, nonlocal treatment of nuclear dynamics.

Initial vibrational state dependence of resonant excitation and ‘‘dissociative attachment’’ in electron–N2 scattering

A beam of vibrationally excited ground state nitrogen molecules has been generated using a microwave discharge. The effect of this vibrational energy on the different decay processes of the A 2Πu state of N−2 formed by electron impact in the 7–13 eV region has been studied using an electron-impact spectrometer. Firstly, the ’’boomerang’’ oscillations occuring in the excitation cross section of the A 3Σ+u levels increase in amplitude when the initial level is v=1. This effect, as well as the measured cross sections are well described by calculations using the local complex potential model. Secondly, the cross section ratio for the ’’dissociative attachment’’, process yielding unstable N−(3P) from the v=0 and 1 levels has been evaluated indicating that the vibrational energy has almost no effect. The calculations further indicate that this ratio only rises to 4 when going from v=0 to 4 which is in sharp contrast to H2 where, in the 4 eV region the same amount of vibrational energy increases the dissociative attachment cross section by a factor of 360.