ESR 11

Thesis title: Laboratory experiments on the gas-phase formation routes of interstellar molecules: neutral-neutral reactions.

Supervisor: Prof. Nadia Balucani (University of Perugia)

Recruitment Institution: University of Perugia, Italy

Doctoral School: University of Perugia, Italy

Mobility: The ESR will spend 6 months at University of Trento under the supervision of Prof. D. Ascenzi.

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:

More than 200 molecules have been detected in the interstellar medium to date. The large majority of them include at least one carbon atom and some of them exhibit a certain degree of complexity (those holding six atoms or more are referred to as interstellar Complex Organic Molecules, iCOMs). Their formation mechanisms are still matter of debate as they can be formed directly in the gas-phase (where they are observed) or in the icy mantles of interstellar grains that can play a catalytic role. Given the harsh conditions of interstellar objects (where the number density can be as low as 10^4 particles/cm3 and the temperature as low as 10 K), only barrier-less reactions are to be considered and, therefore, neutral reactions must involve at least one open-shell species (atomic or molecular radicals).

In our laboratory at the University of Perugia we investigate bimolecular neutral-neutral reactions by means of the crossed molecular beam technique with mass spectrometric detections. The crossed beam technique allows one to investigate chemical reactions in a collision free environment, thus nicely simulating the low number density conditions of the interstellar medium. The crossed beam machine features a radiofrequency discharge beam source which has been successfully used to produce beams of transient species, including C, O, N, S and Cl atoms, as well as OH and CN diatomic radicals.

The focus of the thesis work will be on bimolecular reactions leading to the formation or destruction of iCOMs. The purpose is to establish if the interactions of atomic and molecular radicals (e.g. oxygen and carbon atoms, or OH and CN radicals) are able to degrade those species and their precursors, or if, conversely, they contribute to increase their molecular complexity.

Expected Results: Product branching ratios for reactions involving iCOMs and their precursors. Planned secondment at the University of Trento UNITN for 6 months (from M29).

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.