Binding energies, reactivity, and sputtering processes

It is now recognized that physical and chemical processes can occur on the surface of dust grains through adsorption/desorption processes, surface-catalyzed chemical reactions, and energetic surface processes involving cosmic-rays and ultraviolet radiation. These processes are very crucial in the dense and cold part of the ISM (densities of 10⁴ - 10⁶ cm^-3 and T = 10 K), where dust particles can accrete icy mantles. These mantles are mainly composed of H₂O and in small amounts by other species like CO, CH₄, CO₂, and NH₃.

Key questions in this area of astrochemistry are

• What is the efficiency of molecules formation under ISM conditions?
• How does the chemical composition and the morphology of the surface influence molecules
formation?
• Do complex organic molecules form through surface catalysis or gas-phase routes should be considered?
• How do molecules in spaces relate to life as we know it?
• To which extent are interstellar-chemistry products preserved into planetary systems?

Experimental and theoretical data are fundamental to link observations and models, in particular binding energies, energy barriers, and reaction rates of all the major molecular and atomic species on astronomically relevant surfaces, represent the most relevant data. A quantitative characterization of such processes is only possible through dedicated laboratory studies, i.e. under full control of a large set of parameters such as temperature, atom-flux, and ice morphology.

Our main goals are:

• To measure binding energies of relevant species on the surface of interstellar dust grains
• To study the formation of complex organic molecules and other relevant molecules on the surface of grains
• To study sputtering processes, secondary electrons emission and photoelectric yields under ISM conditions
• To develop high-resolution detectors in the mm/submm, and coupling them with desorption experiments
• To study the size-dependence of all the aferomentioned processes

The short-term goal is to build the trap, test it, characterize one 500 nm nanoparticle of SiO₂ by measuring its mass, and then move the entire setup in a cryogenic chamber. At the same time, with an ion sputtering or an electron gun, sputtering experiments can be performed. Dust sputtering plays a crucial role in AGN-driven ouflows for instance, where destruction and formation of the dust can affect the thermal balance and the formation of molecular gas.

On the long-term we aim to build a gas pipeline to deposit gas-phase molecules on the surface of the trapped particle and measure binding energies and reactivity.