Title: Mutual Neutralization in collisions with oppositely charged fullerene (C60) ions

by Raka Paul (Stockholm University)

Monday 12 Jun 2023, 10:00 → 12:00 Europe/Stockholm

FA31 (AlbaNova Main Building)

In this thesis, results from Mutual Neutralization experiment carried out at DESIREE facility, involving merged interacting ion beams, of oppositely charged C60 ions are presented. This reaction may be of importance for explaining the ionization balance in astrophysical environments, as it defines the chemistry in molecular gas clouds. To interpret the results from the experiment, and for estimating the reaction cross sections as a function of collision energy, the Landau-Zener model is employed, with the electronic excited states of neutral C60 calculated using Time-Dependent Density Functional Theory.
The importance of applying an interacting potential that takes into account mutual
polarization effects and the finite sizes of the collision partners, in the Landau-Zener model is highlighted. Consequences of varying the methods to estimate the electronic couplings between ionic and covalent states is also investigated. We do not observe variation in total cross section with changing coupling elements. A good agreement is observed between the Landau-Zener model and the experiment, the model is applied to calculate the total Mutual Neutralization cross section as a function of center-of-mass collision energy in the (0.0 - 4.98) eV energy range. We find the cross section is almost an order of magnitude larger than what has been reported for H++H− collisions. Thus, it suggests that Mutual Neutralization processes indeed may be important for the charge balance in interstellar molecular clouds where electrons are not the main carriers of negative charges.