Elastic and inelastic low-energy electron collisions with pyrazine

We present results of ab-initio scattering calculations for electron collisions with pyrazine using the R-matrix method, carried out at various levels of approximation. We confirm the existing experimental and theoretical understanding of the three well-known Π* shape resonances. In addition, we find numerous core-excited resonances (above 4.8 eV) and identify their most likely parent states. We also present differential cross sections, showing high sensitivity to the scattering model chosen at low energies. We make recommendations regarding the selection of models for scattering calculations with this type of targets

UKRmol-scripts: a Perl-based system for the automated operation of the photoionization and electron/positron scattering suite UKRmol+

UKRmol-scripts is a set of Perl scripts to automatically run the UKRmol+ codes, a complex software suite based on the R-matrix method to calculate fixed-nuclei photoionization and electron- and positron-scattering for polyatomic molecules. Starting with several basic parameters, the scripts operatively produce all necessary input files and run all codes for electronic structure and scattering calculations as well as gather the more frequently required outputs. The scripts provide a simple way to run such calculations for many molecular geometries concurrently and collect the resulting data for easier post-processing and visualization. We describe the structure of the scripts and the input parameters as well as provide examples for photoionization and electron and positron collisions with molecules. The codes are freely available from Zenodo

Elastic and inelastic cross sections for low-energy electron collisions with pyrimidine

We present theoretical elastic and electronic excitation cross sections and experimental electronic excitation cross sections for electron collisions with pyrimidine. We use the R-matrix method to determine elastic integral and differential cross sections and integral inelastic cross sections for energies up to 15 eV. The experimental inelastic cross sections have been determined in the 15–50 eV impact energy range. Typically, there is quite reasonable agreement between the theoretical and experimental integral inelastic cross sections. Calculated elastic cross sections agree very well with prior results

Benchmark Calculations of Electron Impact Electronic Excitation of the Hydrogen Molecule

We present benchmark integrated and differential cross-sections for electron collisions with H$_2$ using two different theoretical approaches, namely, the R-matrix and molecular convergent close-coupling (MCCC). This is similar to comparative studies conducted on electron-atom collisions for H, He and Mg. Electron impact excitation to the $b \ ^3\Sigma_u^+$, $a \ ^3\Sigma_g^+$, $B \ ^1\Sigma_u^+$,$c \ ^3\Pi_u$,$EF \ ^1\Sigma_g^+$,$C \ ^1\Pi_u$,$e \ ^3\Sigma_u^+$,$h \ ^3\Sigma_g^+$,$B' \ ^1\Sigma_u^+$and$d \ ^3\Pi_u$excited electronic states are considered. Calculations are presented in both the fixed nuclei and adiabatic nuclei approximations, where the latter is shown only for the$b \ ^3\Sigma_u^+$ state. Good agreement is found for all transitions presented. Where available, we compare with existing experimental and recommended data.Comment: 21 pages, 25 figure

A joint theoretical and experimental study for elastic electron scattering from 1,4-dioxane

We present results of measurements and calculations of elastic electron scattering from 1,4-dioxane in the energy range of 0–1000 eV. Absolute differential and integral elastic cross sections have been measured using a crossed electron-molecule beam spectrometer and the relative flow technique, at four energies in the 10–30 eV range and for scattered electrons in the angular range 20°–129°. The measured cross sections are compared with results from R-matrix computations, at the static exchange plus polarization level, calculated at energies between 0–20 eV, and with calculations employing the independent atom model with the screening corrected additivity rule (IAM-SCAR). Those latter computations were conducted at energies between 1 and 1000 eV. Agreement between the measured and R-matrix cross sections was typically found to be good at all common energies, whereas agreement with IAM-SCAR was satisfactory only at 30 eV. To the best of our knowledge, the present results are the first absolute data to be published in the literature for this scattering system

Multidimensional high harmonic spectroscopy of polyatomic molecules: detecting sub-cycle laser-driven hole dynamics upon ionization in strong mid-IR laser fields

High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales. We detect the signatures of laser-driven hole dynamics upon ionization and reconstruct the relative phases and amplitudes for relevant ionization channels in a CO2 molecule on a sub-cycle time scale. Reconstruction of channel-resolved complex ionization amplitudes on attosecond time scales has been a long-standing goal of high harmonic spectroscopy. Our study brings us one step closer to fulfilling this initial promise and developing robust schemes for sub-femtosecond imaging of multielectron rearrangement in complex molecular systems

State Of the Art Report in the fields of numerical analysis and scientific computing. Final version as of 16/02/2020 deliverable D4.1 of the HORIZON 2020 project EURAD.: European Joint Programme on Radioactive Waste Management

Document information Project Acronym EURAD Project Title European Joint Programme on Radioactive Waste Management Project Type European Joint Programme (EJP) EC grant agreement No. 847593 Project starting / end date 1 st June 2019-30 May 2024 Work Package No. 4 Work Package Title Development and Improvement Of NUmerical methods and Tools for modelling coupled processes Work Package Acronym DONUT Deliverable No. 4.