New features in the ionic states of N2O4: Experimental and theoretical study

We present a combined experimental and theoretical study focused on the ionic states of the N2O4 molecule. Experimental results regarding photoionization induced by the synchrotron radiation SOLEIL in the 13.5-15.5 eV energy range were obtained using the electron-ion velocity vector correlation method. The potential energy curves for the dissociation of the N-N bond were computed within ab initio multireference wave functions based methods (CASSCF and CASPT2) for the first electronic states of N2O 4 and N2O4

Isotope Effects in the Predissociation of Excited States of N2+ Produced by Photoionization of 14N2 and 15N2 at Energies Between 24.2 and 25.6 eV

Photoelectron/photoion imaging spectrometry employing dispersed VUV radiation from the SOLEIL synchrotron has been used to study the predissociation of N2+ states located up to 1.3 eV above the ion's first dissociation limit. Branching ratios for unimolecular decay into either N2+ or N+ were obtained by measuring coincidences between threshold electrons and mass-selected product ions, using a supersonic beam of either 14N2 or 15N2 as photoionization target. The results confirm that predissociation of the C2Σu+ state of 14N2+ is faster than emission to the electronic ground-state by a factor 10 or more for all vibrational levels v′ ≥ 3, while for 15N2+ the two decay modes have comparable probabilities for the levels v′ = 3, 4, and 5. In contrast, no significant isotope effect could be observed for the other states of N2+ identified in the photoelectron spectrum. For both 14N2+ and 15N2+ isotopologues all vibrational levels of these other states decay to an extent of at least 95% by predissociation

Roadmap on photonic, electronic and atomic collision physics: I. Light-matter interaction

We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap I, we focus on light-matter interaction. In this area, studies of ultrafast electronic and molecular dynamics have been rapidly growing, with the advent of new light sources such as attosecond lasers and X-ray free electron lasers. In parallel, experiments with established synchrotron radiation sources and femtosecond lasers using cutting- edge detection schemes are revealing new scientific insights that have never been exploited. Relevant theories are also being rapidly developed. Target samples for photon-impact experiments are expanding from atoms and small molecules to complex systems such as biomolecules, fullerene, clusters and solids. This Roadmap aims at looking back along the road, explaining the development of these fields, and looking forward, collecting contributions from twenty leading groups from the field

Circular Dichroism in Molecular Frame Photoemission

International audienceWe report a comparative experimental and theoretical study of circular dichroism in electron angular distribution (CDAD) in the molecular frame (MF) of linear molecules photoionized by circularly or elliptically polarized light. The CDAD is derived from the analysis of the complete molecular frame angular distribution (MFPAD) I(χ,θe,φe), where χ is the orientation of the molecule with respect to the light propagation axis and (θe,φe) the electron emission direction in the MF, using the vector correlation method. The CDAD is quantified by the θe dependence of the left-right emission asymmetry maximum in the plane perpendicular to the light propagation axis k, for a space fixed molecule orthogonal to k. The experimental results for selected valence shell photoionization (PI) reactions in NO, O2, N2O compare very well with the multichannel Schwinger configuration interaction (MCSCI) ab initio calculations. Combined with a simple model of the ionization process, including the partial-wave composition of the initial state and phase shifts estimated from quantum defects for the various scattering partial-waves, these results provide the basis for a general discussion of the circular dichroism effect. This study enables us to disentangle the influence of the (spσ, pπ ...) initial valence shell ionized orbital and that of the scattering dynamics on some fingerprint properties of the CDAD. On the other hand, the CDAD for sσ K shell is purely assigned to a final state scattering effect. This analysis will be extended to PI of non-linear molecules where the circular dichroism characterizes recoil frame photoelectron angular distributions (RFPADs)

Dynamical processes in atomic and molecular physics

Atomic and molecular physics underlie a basis for our knowledge of fundamental processes in nature and technology and in such applications as solid state physics, chemistry and biology. In recent years, atomic and molecular physics has undergone a revolutionary change due to great achievements in computing and experimental techniques. As a result, it has become possible to obtain information both on atomic and molecular characteristics and on dynamics of atomic and molecular processes. This e-book highlights the present state of investigations in the field of atomic and molecular physics. Rec

Vector correlations in dissociative photoionization of small polyatomic molecules

La photoionisation dissociative de petites molécules polyatomiques, ici N20 et CO2, induite par rayonnement synchrotron VUV polarisé linéairement est étudiée par la méthode des corrélations vectorielles, dans les conditions où la photoionisation conduit à un ion, un fragment neutre et un électron. Celle-ci consiste à mesurer les vecteurs vitesses du photoion et du photoélectron produits par chaque événement. Le spectromètre des vitesses utilise la détection en coïncidence de l'ion et de l'électron résolue en temps-de-vol et sensible en position. Les particules chargées sont extraites de la zone d'interaction par un champ électrique uniforme, qui en assure une collection complète. Deux lentilles électrostatiques ont permis d'améliorer la résolution des vecteurs vitesses. Le diagramme de corrélation des énergies cinétiques ion-électron déduit des amplitudes des vecteurs vitesses permet d'identifier le chemin réactionnel pour chaque processus par l'état intermédiaire de valence de N20+ ou CO2+, ou l'état autoionisant N20**, et la limite de dissociation caractérisée par l'état électronique des deux fragments et la distribution vibrationnelle du fragment moléculaire. La corrélation spatiale des deux vecteurs vitesses et de l'axe de la polarisation de la lumière conduit, pour chaque processus, à la dépendance polaire et azimutale de la distribution angulaire des photoélectrons dans le référentiel moléculaire, pour chaque orientation de l'axe moléculaire par rapport à la polarisation. Pour chaque processus les résultats sont représentés par quatre fonctions Fij, qui contiennent l'information la plus complète sur la dynamique de la photoionisation : leur analyse en ondes partielles donne accès aux moments de transition. Pour plusieurs réactions identifiées, la distribution angulaire des photoélectrons dans le référentiel moléculaire présente des anisotropies. Certains résultats obtenus pour N20 sont comparés avec des calculs 'multichannel Schwinger configuration interaction'.Dissociative photoionization of small polyatomic molecules, here N20 and CO2, induced by VUV linearly polarized synchrotron radiation is studied using the vector correlation method, in conditions where photoionization leads to one ion, one neutral fragment, and one electron. The vector correlation method consists in measuring the velocity vectors of the photoion and photoelectron produced in each event. The velocity spectrometer combines time-of-flight resolved and position sensitive ion-electron coincidence detection. Ions and electrons are extracted from the interaction zone by a uniform electric field, which ensures a complete collection of both particles. Electrostatic lenses are implemented in the spectrometer in order to increase the velocity vector resolution. The ion-electron kinetic energy correlation derived from the magnitude of the velocity vectors for the coincident events allows one to identify the reaction pathway for each process, in terms of the intermediate N2O+ or CO2+ valence or inner-valence ionic state, or resonant N20** autoionizing state, and the dissociation limit characterized by the electronic states of both fragments and the vibrational distribution of the molecular fragment. The spatial analysis, correlating the two velocities and the polarization axis of the light, determines, for each process, the polar and azimuthal dependence of the molecular frame photoelectron angular distribution, for any orientation of the molecular axis with respect to the polarization axis. The results are presented in terms of four Fij functions which contain the most complete information about the photoionization dynamics for each process: their partial wave analysis gives access to the transition moments. A large number of reactions are identified, and anisotropies in the photoelectron angular distribution in the molecular frame are observed. Selected results obtained for N2O are compared with multichannel Schwinger configuration interaction calculations.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

CORRELATIONS VECTORIELLES DANS LA PHOTOIONISATION DISSOCIATIVE DE MOLECULES DIATOMIQUES INDUITE PAR LUMIERE POLARISEE

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Three dimensional detection of single metastable helium atoms

PosterYoung Atom Opticians (Poster), Krakow, Polan

Angularly resolved photoionization dynamics in atoms and molecules combining temporally and spectrally resolved experiments at ATTOLab and Synchrotron SOLEIL

International audienceWe report results for XUV-IR two-photon ionization of Ar, Ne, NO, and O2, where an XUV attosecond pulse train is superimposed with a synchronized IR pulse, obtained at the ATTOLab laser facility using electron–ion coincidence 3D momentum spectroscopy. Temporally resolved photoelectron angular distributions providing angle-resolved time-delays for np ionization of Ar and Ne, achieved by reconstruction of attosecond beating by interference of two-photon transitions through a unified formalism (Joseph et al. in J Phys B At Mol Opt Phys 53:184007, 2020), are summarized. For inner valence XUV-IR dissociative photoionization of NO and O2 molecules, we report electron–ion kinetic energy correlation diagrams and disentangle the dissociative photoionization processes relying on parallel XUV experiments at Synchrotron SOLEIL. For ionization into the NO+(c3Π) ionic state, extending the formalism developed for single-photon ionization, we focus on photoelectron angular distributions averaged on the delay between the XUV and the IR field in the field frame, molecular frame, and electron frame of reference