Formation and Reactivity of carbonaceous Aerosols in Planetary Atmospheres – FRAPA

These studies required the construction of a new, original set-up based on the use of a ‘pump-probe’ method applied in the µs-ms range, where an ion beam is used to induce molecular growth creating new molecules, which are further analyzed by a laser beam interacting with the products trapped in a linear electrostatic trap (Zajfman type). Such a method has never been applied for these large systems and promises to obtain original results concerning the stability, lifetime, structure and binding conditions, in particular as the experiments will be accompanied by theoretical calculations.

In the present project, we propose to study particle growth and destruction mechanisms induced by ions colliding with loosely bound C-containing clusters (small hydrocarbon molecules, PAHs molecules, ferrocene, amino-acids, etc;). In the framework of this project, several advances were obtained:

• A development of a novel pump-probe experimental set-up based on an electrostatic trap which allows to prepare complex targets and to clearly identify the final reaction products by tandem mass spectrometry (with two ionising beams: ions as a pump and photons as a probe);

• A theoretical study of 1,3-butadiene cluster structures using different quantum chemical methods;

• An evidence of photon induced formation of prebiotic molecules which are considered as a building blocks of life; e.g. peptide bond formation in the protonated serine dimer following vacuum UV photon‐induced excitation;

• An investigation of fragmentation dynamics of the organometallic ferrocene induced by ion-collision;

• Study of bond breaking and making in mixed clusters of fullerene and coronene molecules induced by keV-ion impact.

The CIMAP laboratory is a multidisciplinary research laboratory where scientific areas span from ion-matter interaction to materials for lasers, photonics and electronics. The proposed project is related to the research activity of the AMA team which is specialised in studies of relaxation mechanisms of excited molecular systems in the gas phase under ion bombardment (stability, dissociation of molecules and clusters, etc). CIMAP is situated in the proximity of different ion beam lines of GANIL – a unique tool to study ion interactions with matter. Experimental set-ups developed at CIMAP can be used at all available beam energies. Moreover, CIMAP is a user facility, which means that local scientists assist external researchers in using the irradiation facilities of GANIL for studies in atomic and molecular collisions, material science, etc. Thus, naturally, once fully commissioned and operational, the set-up proposed in this project will be opened to collaborations with external users via the GANIL-CIMAP facility for periods well beyond the timescale of the present project. Therefore, this proposal will not only contribute to the fields of astrochemistry, astrophysics and atmospheric physics but also to fields which might be related to radiobiology and cancer treatment, as it will be also possible to investigate with the proposed approach ion interactions with functionalized radio-sensitizers and complex biomolecular systems.

The objective of FRAPA project is to better understand the physical and chemical evolution of the atmospheres of planets/moons (e.g. Earth, Titan) and the particle distribution in the interstellar medium . For this it is essential to study the formation, growth and destruction mechanisms occurring in carbon-containing nanoparticles after interaction with ionising radiation. The sizes of carbonaceous particles cover a very large range, from large molecules to nanometer-sized systems. On Earth, Polycyclic Aromatic Hydrocarbons (PAHs) are produced in incomplete combustion and they are key intermediates in the inception and growth of soot particles. In space, carbon particles are primarily formed in the outflows of carbon rich stars, where small carbon chains grow to polycyclic aromatic hydrocarbons or fullerenes. In this bottom-up process these molecules nucleate into larger PAH structures and finally into nanoparticles. However, the origin of the large carbonaceous species and initial heterocyclic skeletal structures of astrophysical nitrogenated or oxygenated PAHs is still unclear. In particular, there is a clear lack of information about ion induced processes in complex nanometric systems.

In the present project, we propose to study particle growth and destruction mechanisms induced by ions colliding with loosely bound C-containing clusters (pure and mixed PAH clusters with water, or ammonia, small hydrocarbon molecules). This requires the development of a novel pump-probe experimental set-up which allows to prepare complex targets and to clearly identify the final reaction products by mass spectrometry (with two ionising beams: ions as a pump and photons as a probe). The aim is to obtain detailed information (size, structure, stability-lifetime od selected species) of the ion-induced reaction products. The project will benefit strongly from theoretical support (in collaboration with LCPQ, Toulouse and UAM, Madrid) and the availability of different beam lines at the GANIL facility (Grand Accélerateur National d’Ions Lourds, Caen, France) allowing to study fragmentation and reactivity of such systems in a very large range of ion kinetic energies from keV to GeV. Thus, different mechanisms due to potential energy, nuclear stopping and/or electronic excitation and ionisation can be probed, mimicking the interaction with solar wind or ions trapped in the Jupiter magnetosphere and cosmic rays. Moreover, we plan to study nucleation of aerosols/grains.

In summary, the proposed studies provide answers to open questions on ion-induced fragmentation dynamics and reactivity of complex molecular systems (e.g. growth, formation of new molecules). These studies are expected to contribute to advances in the fields of astrophysics and astrochemistry (e.g. formation of prebiotic molecules and dust formation) as well as in the field of atmospheric research (nucleation phenomena, aerosol formation, ageing of nanoparticles).