Klaus Bartschat

Complementary imaging of the nuclear dynamics in laser-excited diatomic molecular ions in the time and frequency domains

Experimentally, the bound and dissociative nuclear dynamics in small molecular ions can be resolved in time by using intense ultrashort pump in combination with delayed probe laser pulses. We discuss the modelling of related pump–probe-delay-dependent fragment kinetic-energy-release (KER) spectra for the laser-induced dissociative ionization of selected diatomic molecules and show how the quantum-mechanical simulation of measured KER spectra—in both the time domain and as a function of the beat frequency between molecular vibrational levels—reveals dissociation pathways and the characteristics of initially occupied molecular potential curves.

The B-spline R-matrix method for atomic processes: application to atomic structure, electron collisions and photoionization

The basic ideas of the B-spline R-matrix (BSR) approach are reviewed, and the use of the method is illustrated with a variety of applications to atomic structure, electron?atom collisions and photo-induced processes. Special emphasis is placed on complex, open-shell targets, for which the method has proven very successful in reproducing, for example, a wealth of near-threshold resonance structures. Recent extensions to a fully relativistic framework and intermediate energies have allowed for an accurate treatment of heavy targets as well as a fully nonperturbative scheme for electron-impact ionization. Finally, field-free BSR Hamiltonian and electric dipole matrices can be employed in the time-dependent treatment of intense short-pulse laser?atom interactions.

Electron - atom scattering at low and intermediate energies using a pseudo-state/ R-matrix basis

The use of a pseudo-state expansion within the standard low-energy R-matrix framework to facilitate the study of electron scattering by complex atoms and ions at both low and intermediate energies is discussed. Electron scattering from atomic hydrogen is considered as an example, and results for elastic scattering phase shifts and excitation cross sections are found to be in excellent agreement with recent IERM results in these energy regions. The advantage of this procedure is that existing computer codes, which have been developed over many years, can be directly extended to study electron scattering from a general N-electron target atom or ion.

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Coherent control with a short-wavelength free-electron laser

Researchers demonstrate correlation of two colours (63.0 and 31.5 nm wavelengths) in a free-electron laser and control photoelectron angular distribution by adjusting phase with 3 attosecond resolution.

Uncertainty Estimates for Theoretical Atomic and Molecular Data

Sources of uncertainty are reviewed for calculated atomic and molecular data that are important for plasma modeling: atomic and molecular structures and cross sections for electron-atom, electron-molecule, and heavy particle collisions. We concentrate on model uncertainties due to approximations to the fundamental many-body quantum mechanical equations and we aim to provide guidelines to estimate uncertainties as a routine part of computations of data for structure and scattering.

The R-matrix with pseudo-states method: Theory and applications to electron scattering and photoionization

Abstract Until a few years ago, calculations for electron scattering from atoms and ions were typically performed using nonperturbative close-coupling-type approximations for low impact energies and perturbative Born-type methods in the high—energy regime. Especially for neutral as well as singly and even doubly ionized targets, however, neither one of those methods is particularly reliable for the “intermediate energy regime”, i.e., impact energies near and up to about five times the ionization threshold. This gap has recently been closed by several modifications to the standard close-coupling (R-matrix) formalism. In this paper, the principal ideas behind the R-matrix with pseudo-states (RMPS) method are introduced, and the similarities as well as the differences to related approaches such as the convergent close-coupling (CCC) and the intermediate-energy R-matrix (IERM) methods are discussed. Furthermore, example cases illustrating the need for using such sophisticated approaches are presented.

B-spline calculations of oscillator strengths in neutral argon

B-spline box-based multi-channel calculations of transition probabilities in Ar I are reported for energy levels up to n = 12. An individually optimized, term-dependent set of non-orthogonal valence orbitals is used to account for the strong term dependence in the one-electron orbitals. Energy levels and oscillator strengths for transitions from the 3p6 ground-state configuration as well as for transitions between excited states have been computed in the Breit–Pauli approximation. The agreement in the length and velocity gauges of the transition data and the accuracy of the binding energies are used to estimate the accuracy of our results, which are also compared with experimental and other theoretical data. It is shown that the present method can be used for accurate calculations of oscillator strengths for states with intermediate and high n-values, for which it is difficult to apply standard multi-configuration Hartree–Fock methods.

Complete Experiments in Electron-Atom Collisions

Publisher Summary This chapter addresses the advances made to date in complete electron–atom collision experiments. It presents a series of key examples for fundamental scattering processes, together with the experimental techniques that have been used. The aim of theoretical quantum physics is to model as accurately as possible the development of the system in the interaction region, for the confrontation of predictions with actual observables. For many important processes in nature, typical observables are averages over key parameters, such as incident directions, scattering angle, velocity, temperature, and so forth. However, the ultimate goal is to establish uniquely the relationship between the key vectors,|ψ〉in and |ψ〉out, which determine the initial and final states of the system. The series of examples presented in the chapter shows that the field of quantum mechanically complete experiments has developed to considerable maturity within the area of electron–atom collisions since the time of the formulation of a “perfect scattering experiment” more than 25 years ago.

Near-infrared collisional radiative model for Xe plasma electrostatic thrusters: the role of metastable atoms

Mestastable Xe atoms play an important role in the collisional radiative processes of dense xenon plasmas, including those of electric thrusters for space vehicles. Recent measurements and calculations of electron-excitation processes out of the 5p56s J = 2 metastable state (1s5 state in Paschen notation) have allowed for the development of a collisional radiative model for Xe near-infrared (NIR) emissions based on the population of the metastable level through 2p?1s5 radiative transitions, and based on depopulation through electron-impact excitation. A modified plasma radiative model incorporating newly computed electron-impact excitation cross sections using both relativistic distorted wave and semi-relativistic Breit?Pauli B-Spline R-matrix methods is presented. The model applies to optically thin, low-density regions of the thruster plasma and is most accurate at electron temperatures below 10?eV. The model is tested on laboratory spectral measurements of the D55 TAL and BHT-200 Hall thruster plasma NIR radiation. The metastable neutral fraction is determined to rise from 0.1 to slightly above 1% as the electron temperature increases from ~2 to 10?eV, reaching a maximum around 15?eV. Electron temperatures derived with the modified model are approximately 20% lower than a previous version of the model that used an approximate approach to account for metastable population and line intensity enhancement.