M-C Bacchus-Montabonel

Theoretical study of electron exchange in Mg2+–B collisions

The electron capture of Mg 2+ ions in collisions with boron atoms has been investigated using ab initio quantum chemical approaches. The potential energies of the electronic states implicated in the process together with the non adiabatic coupling matrix elements have been calculated by multi-reference configuration interaction methods. Total and partial cross sections for the charge transfer reaction are determined in the (1–600) keV impact energy range by means of semiclassical approaches. A detailed analysis of the electron capture mechanism taking into account radial and rotational interactions has been performed and compared to previous studies on collision systems involving the Mg 2+ projectile ion.

TRAPPING OF NOBLE GASES BY RADIATIVE ASSOCIATION WITH IN THE PROTOSOLAR NEBULA

The heavy noble gas deficiencies observed in Titans atmosphere and in comets have been proposed to be related to a sequestration process by in the gas phase at the early protosolar nebula. Chemical thermodynamics and astrophysics modeling are favorable to this hypothesis, as presented in preceding papers. However, there is a point still to be raised, i.e., that no dynamical study of the efficiency of the collisional processes had been performed so far. Here, we show that, apart from the expected exception of Ne, the rate constants obtained, i.e., 0.7 × 10−18, 0.5 × 10−16, and 10−16 (cm3 s−1) for Ar, Kr, and Xe, respectively, are reasonably high for such processes, particularly in the case of Kr and Xe. The temperature dependence is also considered, showing a similar behavior for all noble gases with a peak efficiency in the range 50–60 K. Globally, we can conclude that the scenario of sequestration by is definitively comforted by the results of our quantum dynamical treatment. This process may also be responsible of the Ar impoverishment just measured in comet 67P/Churyumov–Gerasimenko by the ROSINA mass spectrometer on board the Rosetta spacecraft.