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Discovering the origin of extraterrestrial molecules

Since the first discovery of water and ammonia in the interstellar medium more than 50 years ago, the number of molecules that have been detected in various regions of space has increased rapidly thanks to advances in telescope sensitivity and spatial resolution. So far more than 200 different molecules have been detected and that number is continuing to increase (see and

Astronomers use molecules as a tool to infer information about the structure, dynamics and evolution of astronomical objects. For instance, the chemical composition of Solar-like planetary-forming systems can be used to unveil the history of our Solar System. To achieve this, an interdisciplinary approach is required, with astronomical observations being supported and interpreted via laboratory experiments and physical/chemical models of interstellar environments.

This is the topic of the H2020 MSCA Innovative Training Network ACO (AstroChemicalOrigins), which involves several European institutions and companies, of which our group is a node.

Of particular interest are the so called “prebiotic” molecules, small organic species (such as amides, alcohols, cyanides) that are the building blocks of amino acids, sugars and other biomolecules. Several prebiotic molecules have been detected in interstellar gas and circumstellar shells, thereby demonstrating that such molecules are produced in the early stages of solar system formation.

Discoveries such as these help to increase our understanding of the origins of life on our own planet, with one fascinating idea being that interstellar objects can act as “chemical factories” from which the molecular building blocks of life (as we know it) could have been delivered to the primitive Earth by comets, meteorites and asteroids. The presence of complex molecules in regions of extreme temperature and pressure represents a great challenge to our understanding of chemical reactivity, and our research aims to unveil the formation and destruction routes of increasingly complex molecules. This is done by studying the reactivity of by charged species under conditions (with regards to pressure and collision energy) as close as possible to those present in space.

The experimental set-up in our laboratory uses tandem guided ion beam mass spectrometry to measure absolute cross sections and product branching ratios as a function of collision energy for a variety of ion-neutral reaction systems (including specific isomers) in the gas phase under single collision conditions.

We also work in collaboration with scientists from CNRS-University Paris Saclay (R. Thissen, C. Alcaraz and C. Romanzin), where a similar experimental set-up, used in combination with VUV synchrotron radiation, allows to extend the range of ions that can be studied by generating cations with a defined amount of internal energy through the controlled dissociative photoionisation of various neutral precursors.

Additionally, though the majority of astronomical molecules are composed of the cosmically abundant biogenic elements H, C, N and O, several molecules have been detected containing heavier elements. A recently funded interdisciplinary project (PRIN2020 – Astrochemistry beyond the second period Elements) is focused on exploring the formation routes of molecules containing atoms beyond the second period of the Periodic Table, with a particular focus on both S and P, due to their prebiotic relevance, as well as Si and Cl, due to the lack of known routes for their incorporation in astrochemical molecules. The project employs an interdisciplinary approach (kinetics and dynamics experiments/spectroscopy/computational techniques/astronomical observations) and involves research groups from the Universities of Perugia (Nadia Balucani), Torino (Piero Ugliengo), Bologna (Sonia Melandri) as well as astronomers from the INAF institute in Arcetri (C. Codella and L. Podio).