The complementarity of the two levels of theoretical mean-field description complemented by new gas phase experiments will contribute to a deeper understanding of the fundamental mechanisms underlying energy-selective dissociations of molecules of biological interest, dissociations mediated by the attachment of beta-particles of low energy.
Understanding the interaction of low energy beta particles (electrons, ß-, and positrons, ß+), constitutes a key subject of fundamental importance in various fields of science. Still, the short timescale dynamics of the ß particle interaction and the complete subsequent fragmentation mechanisms are far from being fully elucidated. This is why the European Community keeps on encouraging these upstream fundamental investigations. <br />The last 2 decades have seen the major impetus to investigate processes induced by low energies (<30 eV) electrons, LEE. Their ability to induce energy-resonant dissociation of molecules in their ground state is established and known as Dissociative Electron Attachment. Experimentally, information mostly relies on the detection of the negative fragments and very few direct measurements exist for the neutral counterparts. Even less studies are found on the gas phase interaction of LEE with molecules prepared in a specific electronic or vibrational mode while they would offer high potentiality for applications such as energy-selective chemistry. <br />Positrons are used for the characterization of material or as medical imaging technique. How matter may be modified after being irradiated by positrons, more particularly low energy ß+ (LEß+), is by far less documented than for LEE. To the best of our knowledge, no real-time calculation of the collision dynamics between a positron and a molecule has been reported yet. <br />This project aims at elucidating at a nanoscale the attachment of LEE or LEß+ to state-selected molecules in the gas phase and their possible subsequent fragmentation thereof. A particular attention will be paid on the dynamics of the attachment process through real-time and real-space mean-field-based calculations and the comparison with new measurements of the neutral and the charged fragments.
This project, at the same time theoretical and experimental, aims at elucidating at a molecular level the attachment of low-energy beta particles, i.e. électrons (LEE) or positrons (LEß+), to gas phase molecules and their possible subsequent fragmentation. It is organized into 3 workpackages (WP). WP1 et WP2, on LEE, directly compare theoretical calculations and experimental measurements, while WP3 focuses on the theoretical implementation of ß+ interaction with electronic systems.
In particular, we study the nature of the resonances, their energy and their possible fragmentation paths, accessible through computations of static properties via state-of-the-art ab-initio techniques and computations of short-time dynamics that describe the attachment process via real-time and real-space mean-field-based theories.
Expérimentally, energy-selection of the target molecule prior to its interaction with a LEE is finely performed by application of a nanosecond and frequency-accordable laser. The possibility to measure all fragments, charged and neutral, will give access to cross-sections scarcely measured up to now.
LPT : Adaptation of the STDHF routines in the 3D code to simulate the electron attachment to a target-moleule (water, furan, pyrazole). Study of the numerical parameters (box size, initial energy and position of the incident electron, physical parameters of the electron, etc.). First results on attachment probability, computed with the new STDHF routines (in particular, with fully dynamical wave functions) obtained and in agreement with those obtained in 2017, however not strictly identical, since the wave functions of the target-molecule were purely static. Study of larger molecules (furan and pyrazole) in progress.
IP2I (ex-IPNL) : Despite asbestos removal of the experimental room and a lockdown enforced from March to June 2020, experimental setup assembled before beginning of lockdown.
First 18 months of WP1 : design and development of the dedicated experimental setup, and tests, in particular of the control/command system. Tests of beam alignment to anticipate WP2 (integration of the laser system). Control/command program of the expertimental setup operational.
Signal acquisition system in progress (slow down by the lockdown).
Independent functioning of the various parts.
ILM : A new methodology to compute electron attachment resonance energies developed and process of validation in progress (benchmark). This methodology is based on the calculations of excited states in LR-TDDFT without the use of empirical parameters.
LPT : Modification of the 3D code to account for an excited state of the target molecule as an input, instead of a ground state. In particular, the case of the excitation by an ultrashort laser pulse (already implemented but to simulate a dynamics initiated by this laser) will be explored. Comparison with the excited states computed by ILM and with the experimental measurements performed by IP2I.
IP2I (ex-IPNL) : The experimental setup is built and functional. Validation of the whole experimental setup (Nov.-Dec. 2020). Integration of the laser system during the second trimester 2021.
ILM : Prediction of the electron attachment resonance energies and characterisation of the electronic excited states of the molecules studied in the experiment (energy level, state character).
No publication nor patent.
Preparation and submission of 2 Hubert Curien projects: IP2I-University Hassan-II of Casablanc (Marocco) et IP2I- University of Siedlce (Poland).
Scientific meetings : 1 Poster et 2 oral communications in international conferences or workshop.
Others : Organisation of an international workshop in Toulouse (Nov. 2019) and finalisation of the release to the community of the LPT 3D code by end of 2020 (https://git.irsamc.ups-tlse.fr/ClusterDynamics/QDD)
The present intertwined Theory/Experiment “Beta-particle Attachment to Molecules of Biological Interest” (BAMBI) project aims at elucidating at the molecular level the dynamics of the attachment of low-energy low-energy beta particles, i.e., electrons (LEE) or positron (LEß+) to molecules in the gas phase and their possible subsequent fragmentation thereof.
BAMBI is divided in three workpackages (WP). WP1 and WP2, concerning LEE, directly compare theoretical calculations with experimental measurements, while WP3 focuses on the theoretical implementation of ß+ interaction with electronic systems in the codes developed by LPT and ILM, with the possibility of an experimental study by IPNL at best during the last year of the project, or more realistically after its completion. The complementarity of the two levels of theoretical mean-field description complemented by new gas phase experiments will contribute to a deeper understanding of the fundamental mechanisms underlying energy-selective dissociations of molecules. A particular attention will be paid on the nature of the resonances, their energy and the accessible fragmentation pathways obtained from state-of-the-art ab initio computations of static properties, and on the short-time dynamics of the attachment process through real-time and real-space mean-field-based calculations.
For LEE, IPNL will develop an experimental state-of-the-art setup capable of measuring the negative fragments and the associated charged and neutral counterpart(s), while keeping their correlation (WP1). This will allow us to have a more complete picture of the Dissociation Electron Attachment (DEA) and to quantify the branching ratios for competitive fragmentation channels, as well as the DEA cross-sections. Obtaining such information is a major advancement to improve the comprehension of reactions in irradiated condensed media, and this will certainly contribute to future innovating approaches of synthesis chemistry and increase fundamental knowledge in fields such as astrochemistry.
To investigate Laser-Assisted DEA to molecules in the gas phase (WP2), a field still in its infancy, IPNL will develop an original pump(laser)-probe(electron) with a tunable laser in the 200nm-2000nm range for molecular excitation with the possibility to delay the laser/electron pulses. Coupled to the LPT and ILM calculations on the same molecular systems, the comparison of the impact of the electronic excitation prior to the interaction with the probing LEE to the case without excitation (WP1) will shed light on the mechanisms at the origin of the enhancement observed in DEA cross-sections, and even on the identification of new fragmentation mechanisms. The new expected information will certainly open new strategies in fields such as nanoscale synthesis chemistry and nanofabrication or lithography which are already in the early stages of development. Transfers of innovative instrumental developments or technologies to different industrial activities (e.g., analytical chemistry) can also be envisioned.
The understanding of the physics of interaction of LEß+ and subsequent physical chemistry is even more at the dawn of its development, especially what concerns molecules of biological interest. Taking advantages of previous theoretical works on the static calculations of cross-sections of collisions positron-atom or -molecule, the outcomes of BAMBI will be new implementations of the position-electron interaction in the same mean-field-based approaches used by ILM and LPT for the study of LEE, thus allowing the comparison of LEE- or LEß+ induced resonance scenarios in systems of biological and astrophysical relevance. Emerging fields as radiation “theranostic” therapy that combines radionuclide-targeted therapy with diagnosis, in which positrons are undeniably the appropriate particles, will also benefit from the findings of BAMBI.
Madame Thi Phuong Mai Dinh (Centre National de la Recherche Scientifique - LABORATOIRE DE PHYSIQUE THEORIQUE)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IPNL - CNRS Institut de Physique Nucléaire de Lyon
CNRS - LPT Centre National de la Recherche Scientifique - LABORATOIRE DE PHYSIQUE THEORIQUE
ILM - CNRS INSTITUT LUMIERE MATIERE
Help of the ANR 509,058 euros
Beginning and duration of the scientific project: December 2018 - 48 Months