Formation of Molecular Hydrogen and Water on Warm Grains

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This investigation will study the formation of molecular hydrogen and water on warm (T50 K) analogs of grains in the interstellar medium (ISM). The researchwill use state-of-the-art techniques to recreate in the laboratory the processes associated with the formation of these molecules on dust grains in space environments. Over the years, the Principal Investigator (PI) has built a group of collaborators who will: 1) provide characterized analogs of dust grains; 2) build ab-initio potentials to study the radical-surface interaction; and 3) implement stochastic methods to use laboratory derived quantities in models of the chemical evolution of space environments. This project is about the formation of two molecules: hydrogen (H2) and water. Molecular hydrogen - the most abundant molecule in space - is made almost exclusively on dust grains. The PI's laboratory conducted the first studies of hydrogen formation on dust analogs (amorphous and crystalline silicates, amorphous carbon and water ices) at low (5-30 K) temperature. But it is known that molecular hydrogen is also formed in environments where the dust temperature is higher (such as in protoplanetary disks) and that different mechanisms operate in these conditions. This project will extend the previous work by targeting the formation (mechanisms and efficiencies) of H2 formation on surfaces of amorphous silicates, polycyclics aromatic hydrocarbons, and graphitic carbon. There are currently no comprehensive studies of H2 formation on dust grain analogs at high (T50K) temperature.Water is a well-recognized pre-requisite for the complex chemistry linked to the emergence and sustainability of life; Interactions of atoms in the gas-phase cannot explain its abundance in the interstellar medium so it is hypothesized that water forms on the surface of interstellar dust grains. This research group is currently completing an NSF-sponsored study of the formation of water via the reaction of hydrogen and oxygen atoms with amorphous silicates and graphite at low temperature. This project will extend the investigation to water formation on grains at higher temperature (as, for example, in protoplanetary disks. This topic is important in understanding the delivery of water to and its incorporation in planets.