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Results for “electron-molecule scattering”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Second order Møller-Plesset and coupled cluster singles and doubles methods with complex basis functions for resonances in electron-molecule scattering

The method of complex basis functions is applied to molecular resonances at correlated levels of theory. Møller-Plesset perturbation theory at second order and equation-of-motion electron attachment coupled-cluster singles and doubles (EOM-EA-CCSD) methods based on a non-Hermitian self-consistent-field reference are used to compute accurate Siegert energies for shape resonances in small molecules including N 2 - , CO - , CO 2 - , and CH 2 O - . Analytic continuation of complex θ-trajectories is used to compute Siegert energies, and the θ-trajectories of energy differences are found to yield more consistent results than those of total energies. Furthermore, the ability of such methods to accurately compute complex potential energy surfaces is investigated, and the possibility of using EOM-EA-CCSD for Feshbach resonances is explored in the context of e-helium scattering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Department of Energy Project DE-SC0012198: Probing Electron-Molecule Scattering with HHG: Theory and Experiment (Final Report)

The study of the motion of atoms in molecules is important to understanding many areas of physical and life sciences. Such motion occurs on many different times scales, with electronic motion occurring on a sub-femtosecond time scale, and simple vibrational motion in tens to hundreds of femtoseconds. One way to follow such processes in real time is by the use of shortpulsed lasers, and in particular by studying time-resolved photoionization and the related process of high-harmonic generation (HHG). Thus there has been much effort to develop the tools necessary to probe molecular systems using short pulse lasers and understanding the sensitivity of the different possible probes to the time dependent geometric structure as well as the electronic structure of molecules. Our research has particularly focused on the connection between high-field processes and the more traditional weak field photoionization processes. Strong field and weak field processes can be connected through models that involve the same matrix elements. We have demonstrated in our study of HHG from SF 6 that the spectrum is sensitive to the interplay between the angular dependence of the ionization step and recombination step. In our study of rescattering spectroscopy, we have shown that with a combination of experiment and theory, we can use this high-field spectroscopy to determine molecular structure in molecules such as C 2 H 4 . We have also developed new computational tools based on overset grids to enable studies on larger molecular systems which use much more robust numerical approaches so that the resulting code can be a tool that non-specialists can use to study related systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Competing ionization and dissociation: Extension of the energy-dependent frame transformation to the gerade symmetry of H 2

This article solves two major tasks that frequently arise in the theory of electron collisions with a target molecular cation. First, it extends the energy-dependent frame transformation (EDFT) treatment, which is needed to map fixed-nuclei electron-molecule scattering matrices into an energy-dependent laboratory-frame scattering matrix with vibrational channel indices. The EDFT mapping can now be carried out even when the target molecule possesses multiple low-energy potential curves, significantly transcending previous applications. Second, it implements a method to extract the rest of the full laboratory-frame scattering matrix, i.e., the columns and rows describing input and/or output dissociation channels. The treatment is benchmarked in this article against the essentially exact solution of a refined two-dimensional model of the singlet gerade Σ symmetry of H 2 . Our tests demonstrate that the theory accurately maps fixed-nuclei scattering information, of the type provided by existing electron-molecule computer codes, into a laboratory-frame scattering matrix that includes both ionization and dissociation. Furthermore, this treatment can provide a general framework applicable to a broad class of electron collision processes involving diatomic target ions, suitable for an accurate description of challenging processes such as dissociative recombination.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Overset-Grid Method with Smooth Orbital Partitioning for Molecular Scattering Calculations

To solve molecular photoionization and electron scattering problems, we use an overset-grid representation of electronic continuum functions, which has an extended central spherical grid that overlaps small spherical grids (subgrids) centered on each atom of a polyatomic molecule. Here, in this work, we present an improved algorithm that smoothly partitions the total wave function between the central grid and the atomic subgrids. The smooth partitioning allows one to use approximately one-fourth the number of partial waves on the central grid compared to our previous implementation with switching functions. The resulting numerical method for treating electron scattering and photoionization of polyatomic molecules combines the accuracy and flexibility of pure numerical grid representations with the rapid convergence of hybrid combinations of atom-centered basis-set expansions and grid methods. The overset-grid representation is implemented using the complex Kohn variational principle for scattering and photoionization amplitudes. The faster convergence with respect to the number of central grid partial waves is demonstrated and accuracy is verified by comparisons with the previous implementation and with far more computationally demanding single-center numerical expansions in electron-molecule scattering and photoionization calculations on the neon dimer (Ne 2 ) system, carbon tetrafluoride (CF 4 ) molecule, and the pyridine (C 5 H 5 N) molecule in the static-exchange approximation.

Molecules↗
DOE OSTI2018

Interference in electron–molecule elastic scattering

General formulas describing the multiple scattering of electron by polyatomic molecules have been derived within the framework of the model of non-overlapping atomic potentials. These formulas are applied to different carbon molecules, both for fixed-in-space and randomly oriented molecules. Here, the molecular continuum wave function is represented as a plane wave plus a linear combination of the Green’s functions for free motion and the derivatives of these functions. Far from the target the electron spherical waves interfere as in the case of the Young’s double slits experiment. This interference manifests itself as diffraction oscillations in the differential and total cross sections for elastic electron scattering. The amplitude of electron scattering by a molecule is defined by the phase shifts for each of the atoms forming the target and its geometry. The numerical calculation of the scattering amplitude in closed form (rather than in the form of S-matrix expansion) is reduced to solving a system of algebraic equations. The number of atoms in a molecule and the atomic phase shifts for the orbital angular momenta included in the calculation define the number of equations.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Electrondriven processes in polyatomic molecules

This project developed and applied scalable computational methods to obtain information about low-energy electron collisions with larger polyatomic molecules. Such collisions are important in modeling radiation damage to living systems, in spark ignition and combustion, and in plasma processing of materials. The focus of the project was to develop efficient methods that could be used to obtain both fundamental scientific insights and data of practical value to applications.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

The interaction of low-energy electrons with fructose molecules

Using a hypocycloidal electronic spectrometer, the interactions of low energy electrons (0–8.50 eV) with fructose molecules, namely, electron scattering and dissociative attachment, are studied. The results of these studies showed that the fragmentation of fructose molecules occurs effectively even at an electron energy close to zero. In the total electron-scattering cross section by molecules, resonance features (at energies ~3.10 and ~5.00 eV) were first observed near the formation thresholds of light ion fragments OH{sup –} and H{sup –}. The correlation of the features observed in the cross sections of electron scattering and dissociative attachment is analyzed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Electron impact ionization in plasma technologies; studies on atomic boron and BN molecule

Electron impact ionization plays important role in plasma technologies. Relevant cross sections on atomic boron are required to understand the erosion processes in fusion experiments. Boronization of plasma exposed surfaces of tokomaks has proved to be an effective way to produce very pure fusion plasmas. This paper reports comprehensive theoretical investigations on electron scattering with atomic Boron and Boron Nitride in solid phases. Presently we determine total ionization cross-section Q{sub ion} and the summed-electronic excitation cross section ΣQ{sub exc} in a standard quantum mechanical formalism called SCOP and CSP-ic methods. Our calculated cross sections are examined as functions of incident electron energy along with available comparisons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Ion-momentum imaging of dissociative attachment of electrons to molecules

Here, we present an overview of experiments and theory relevant to dissociative electron attachment studied by momentum imaging. We describe several key examples of characteristic transient anion dynamics in the form of small polyatomic electron-molecule systems. In each of these examples the so-called axial recoil approximation is found to break down due to correlation of the electronic and nuclear degrees of freedom of the transient anion. Guided by anion fragment momentum measurements and predictions of the electron scattering attachment probability in the molecular frame, we demonstrate that accurate predictions of the dissociation dynamics can be achieved without a detailed investigation of the surface topology of the relevant electronic states or the fragment trajectories on those surfaces.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Attosecond time delays in the body frame for photodetachment from molecular anions

Attosecond time delays in molecular photoionization at low energies are dominated by the contribution of the Coulomb phase, which diverges as the energy of the photoelectron decreases towards zero. With calculations on core-electron ejection from CN – and C 2 – we demonstrate that in photodetachment of molecular anions the absence of the long-range Coulomb interaction in the final state can reveal the delays of narrow low-energy shape resonances that do not generally occur in photoionization. Delays of several femtoseconds can be associated with such resonances. Finally, the angular dependence of photodetachment time delays in the body frame is highly sensitive to short-range anisotropies in the electron-molecule interaction as well as to the initial state.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Resonant spectra of multipole-bound anions

In multipole-bound anions, the excess electron is attached by a short-range multipole potential of a neutral molecule. Such anions are prototypical marginally bound open quantum systems. In particular, around the critical multipole moment required to attach the valence electron, multipole-bound anions exhibit critical behavior associated with a transition from bound states dominated by low-ℓ partial waves to the electron continuum. In this work, multipole-bound anions are described using a nonadiabatic electron-plus-rotor model. The electron-molecule pseudopotential is represented by a short-range multipole field with a Gaussian form factor. The resulting coupled-channel Schrödinger equation is solved by means of the Berggren expansion method, in which the electron's wave function is decomposed into bound states, narrow resonances, and the nonresonant scattering continuum. We show that the Gaussian model predicts the critical transition at the detachment threshold. Resonant states, including bound states, decaying resonances, subthreshold resonances, and antibound states are studied, and exceptional points where two resonant states coalesce are predicted. Furthermore, we discuss the transition of rotational band structures around the threshold and study the effects of channel coupling on the decay width of resonant poles.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Validity of the Born-Oppenheimer approximation in the indirect-dissociative-recombination process

An alternative method is introduced to solve a simple two-dimensional model describing vibrational excitation and dissociation processes during the electron-molecule collisions. The model works with one electronic and one nuclear degree of freedom. The two-dimensional R matrix can be constructed simultaneously on the electronic and nuclear surfaces using all three forms developed previously for electron-atom and electron-molecule collisions. These are the eigenchannel R-matrix form, inversion technique of Nesbet and Robicheaux, and the Wigner-Eisenbud-type form using expansion over the poles of the symmetrized Hamiltonian. The 2D R-matrix method is employed to solve a simple model tailored to describe the dissociative recombination and the vibrational excitation of H 2 + cation in the singlet ungerade symmetry 1 Σ u . These results then serve as a (near-exact) benchmark for the following calculation in which the R-matrix states are replaced by their Born-Oppenheimer approximations. Furthermore, the accuracy of this approach and its correction with the first-order nonadiabatic couplings are discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗