Dissociative electron attachment and vibrational excitation ofH2by low-energy electrons: Calculations based on an improved nonlocal resonance model. II. Vibrational excitation

Abstract

We treat vibrational excitation of hydrogen by low-energy electrons using an improved nonlocal resonance model. The model is based on accurate ab initio data for the 2 ⌺ u + shape resonance and takes full account of the nonlocality of the effective potential for nuclear motion. Integral vibrational excitation cross sections were calculated for numerous initial and final rovibrational states of the hydrogen molecule, and the dependence of the vibrational excitation cross section on the rovibrational initial target state has been investigated. The vibrational excitation cross sections are in very good agreement with measurements for the transitions v =0 → 1 and v =0→ 2, while for higher vibrational channels the agreement is less satisfactory. However, the oscillatory structures in v =0→ 4 vibrational excitation and higher channels predicted by Domcke and collaborators and measured by Allan are described by the present calculation, in very good agreement with the experimental data. A detailed analysis of the origin of the oscillations has been performed. It is shown that the oscillations can be qualitatively understood within the so-called boomerang model of Herzenberg. The resonance contribution to the vibrationally elastic scattering ͑v → v͒ is also discussed. It is found that this cross section is dominated at low energies by the resonance contribution, as predicted by Schulz. The calculated integral vibrational excitation cross sections generally are in good agreement with other theoretical data obtained by different approaches. A comprehensive study of the effect of isotopic substitution has been performed, and an inverse isotope effect in vibrational excitation has been found for certain vibrational levels of the target.

Simple systematization of vibrational excitation cross-section calculations for resonant electron-molecule scattering in the boomerang and impulse models

“…This simple and appealing classification of molecular resonances has, however, been repudiated by computational 18 /experimental 19 demonstration of structure in higher vibrational excitation cross-sections of e-H 2 scattering later substantiated by other investigations [20][21][22] as well. Since the resolution of structure in energy profiles is controlled by decay pattern in the time domain 23 and a time dependent wave packet ͑TDWP͒ formulation of the resonant electronmolecule scattering is available, 11 it is our purpose in this paper to apply the TDWP approach to e-H 2 scattering to investigate the features which control the lack of structure in vibrational excitation cross-sections 1←0 ͑E͒ and 2←0 ͑E͒ but lead to increasingly pronounced structure for 3←0 ͑E͒, 4←0 ͑E͒, 5←0 ͑E͒, and 6←0 ͑E͒ in e-H 2 scattering, to see if the TDWP results can reproduce the details obtained earlier using time independent scattering theory.…”

Molecular Physics of Elementary Processes Relevant to Hypersonics: Electron-Molecule Collisions

“…This has resulted in a vast theoretical and experimental literature on the topic, stimulated by the importance of hydrogen plasmas for both astrophysical and technological research. Sets of cross sections and rate coefficients have been calculated for H 2 (υ i ) by different authors [40][41][42][43][44] for dissociative attachment and vibrational excitations according to the reactions, [42,[46][47][48].…”

Rovibrationally Resolved Time-Dependent Collisional-Radiative Model of Molecular Hydrogen and Its Application to a Fusion Detached Plasma

“…Cross-sections for the transition from (v = 0, J = 0) → (v = 1 ∼ 6, J = 0) in the electronic ground state X 1 Σ + g are calculated up to 6 eV by considering H − 2 (X 2 Σ + u ) resonance [54] (see Figure 3). Their rate coefficients are included in the present model.…”

“…transitions are obtained by assuming that their ratios as the same as their cross-sections at 4 eV given in [54]. We assume that the rate coefficients for (v, J = 0) → (v + 1, J = 0) (v > 6) are the same as that for (v = 6, J = 0) → (v = 7, J = 0).…”

“…In the transitions in [54], the rotational state is fixed. We include (v = 0, J) → (v = 1 ∼ 14, J = J, J ± 2) and (v, J) → (v = v + 1, J = J, J ± 2) in the model assuming the cross-sections for ∆J = 0, ±2 transition are the same.…”