ESR 12

Thesis title: Laboratory experiments and theoretical computations on the gas-phase destruction routes of interstellar molecules: ion-neutral reactions.

Supervisor: Prof. D. Ascenzi (University of Trento)

Recruitment Institution: University of Trento, Italy

Doctoral School: University of Trento, Italy

Mobility: The ESR will spend 6 months at University of Perugia (Italy) under the supervision of Prof. Nadia Balucani.

Eligibility: European and non-European students who not have resided or carried out their main activity (work, studies, ect.) in Italy for more than 12 months in the 3 years immediately before the recruitment date.

Thesis description:

The gas phase chemistry prevailing in the ISM is mainly confined to two-body processes with no activation barriers. Reactions involving ions, being often barrier-less, are feasible in such low-temperature environments, and thus are important reactions of the astrochemical reaction networks. Ion reactions can play a role in the formation and destruction routes of iCOMs (interstellar Complex Organic Molecules). While several scenarios have been explored for their formation via grain and gas-phase processes, reliable experimental data on the rate constants and product branching ratios of ion induced destruction pathways are mostly uncharted.

The thesis project aims at revising existing kinetic parameters (rate coefficients and branching ratios) for ionic reactions, focusing on those that are not included in astrochemical networks or whose parameters are only estimated using oversimplified models or analogies with similar chemical systems. Bimolecular reactions involving ions and iCOMs will be studied using the guided ion beam mass spectrometric method in an octupolar ion guide, under single collision conditions. The technique permits to measure absolute integral reactive cross sections and branching ratios (with detection of the charged products) as a function of collision energy. Experimental data will be complemented by theoretical modelling (carried out in collaboration with other ACO nodes) to obtain realistic estimates of the rates at temperatures relevant for the interstellar medium, explicitly taking into account anisotropies in the potential energy surface and relative orientation of reactants. The aim is to quantify the extent of fragmentation and the nature of products by interactions of interstellar organics with ions and to obtain kinetic parameters to be included in models developed by members of the ACO team.

The thesis is part of the ACO network, whose ultimate goal is to reconstruct the early history of the Solar System by comparing presently forming solar-type planetary systems with its small bodies. The comparison will be based on the most advanced astrochemical knowledge, which will be developed by the interdisciplinary ACO team.