Ultrafast electro-nuclear dynamics of H2 double ionization

The ultrafast electronic and nuclear dynamics of H2 laser-induced double ionization is studied using a time-dependent wave packet approach that goes beyond the fixed nuclei approximation. The double ionization pathways are analyzed by following the evolution of the total wave function during and after the pulse. The rescattering of the first ionized electron produces a coherent superposition of excited molecular states which presents a pronounced transient H+H- character. This attosecond excitation is followed by field-induced double ionization and by the formation of short-lived autoionizing states which decay via double ionization. These two double ionization mechanisms may be identified by their signature imprinted in the kinetic-energy distribution of the ejected protons

Pugwash : les physiciens, l’arme nucléaire, la responsabilité des scientifiques

National audienceDans les années qui suivirent la Seconde Guerre mondiale, les physiciens réalisèrent que la bombe qu’ils avaient construite était en train de leur échapper. Afin de promouvoir un usage pacifique de la science, ils fondèrent le Mouvement Pugwash, qui agit en coulisse en faveur de la paix dans le monde et a été l’un des instigateurs du traité sur la non-prolifération. Il a reçu en 1995 le prix Nobel de la Paix, et encore récemment a contribué à convaincre le gouvernement syrien de détruire ses armes chimiques.L’évolution actuelle est à l’ouverture, vers les scientifiques de toutes disciplines, mais aussi vers un large public qui doit être informé et associé à la réflexion sur les conditions de survie de l’humanité, et de sa survie en paix

Pump-probe dissociative ionization of Nal and Csl aggregated CH3CN

International audienceRecent experiments have investigated the dissociative ionization of NaI and CsI, each aggregated with a molecule of acetonitrile CH3CN, using two femtosecond laser pulses. The first, the pump pulse, excites the NaI or CsI diatom to a dissociative state. The second, the probe pulse, then ionizes the sodium or cesium atom after a variable delay time, and the resulting ion is detected. In the case of NaI, the ion signal is characterized by a single maximum. For CsI, however, an oscillatory signal is observed. By performing two-dimensional wave packet propagations, we are able to reproduce this behavior, which can be explained using simple physical arguments

The short-range reaction matrix in MQDT treatment of dissociative recombination and related processes

We discuss the Lippmann-Schwinger equation which governs the short-range reaction matrix (K-matrix) in the two-step multichannel quantum defect theory (MQDT) of dissociative recombination and related processes. We show that, if the energy dependence of the electronic coupling between the dissociative state and the ionization continua can be neglected, the convergence of the Born expansion of the Lippmann-Schwinger equation is achieved at second order. For the case of energy-dependent interaction, higher order effects are tested using a non-perturbative method for solving the Lippmann-Schwinger equation. Numerical examples are given for the dissociative recombination and vibrational de-excitation of the H$_{2}^{+}$ molecular ion

Rotational effects in low energy dissociative recombination of diatomic ions

The effect of rotational interaction in the low energy dissociative recombination process of diatomic molecules has been explored for typical molecular ions ($\mathrm {H_2^+,\ HD^+,\ OH^+\ and\ NO^+}$) which sample a large range of molecular masses. We show that rotation plays a role mainly for the indirect recombination process through bound Rydberg states, and for light molecules. When the direct process based on a strong electronic interaction is fast and dominating, rotational couplings can be safely neglected especially for heavier molecules like NO