Formation of Molecular Hydrogen and Water on Warm Grains

这项研究将研究在星际介质（ISM）中温暖的（T50 K）类似物颗粒上分子氢和水的形成。这项研究将使用最先进的技术在实验室中重现与太空环境中尘埃颗粒上这些分子形成相关的过程。多年来，首席研究员（PI）已经建立了一个合作者小组，他们将：1）提供尘埃颗粒的特征类似物; 2）建立从头算势来研究自由基-表面相互作用; 3）实施随机方法，在空间环境化学演化模型中使用实验室导出的量。这个项目是关于两个分子的形成：氢（H2）和水。分子氢--太空中最丰富的分子--几乎完全由尘埃颗粒组成。PI的实验室进行了在低温（5-30 K）下对尘埃类似物（无定形和结晶硅酸盐，无定形碳和水冰）形成氢的第一次研究。但众所周知，分子氢也可以在尘埃温度较高的环境中形成（例如在原行星盘中），并且在这些条件下有不同的机制。该项目将通过针对无定形硅酸盐，多环芳烃和石墨碳表面上的H2形成的形成（机制和效率）来扩展以前的工作。目前还没有关于在高温（T50 K）下尘埃颗粒类似物上形成H2的全面研究。水是公认的与生命的出现和可持续性相关的复杂化学的先决条件;气相中原子的相互作用不能解释其在星际介质中的丰度，因此假设水形成于星际尘埃颗粒的表面。该研究小组目前正在完成一项由NSF赞助的研究，即通过氢原子和氧原子与无定形硅酸盐和石墨在低温下反应形成水。该项目将把研究范围扩大到在较高温度下（例如，在原行星盘中）在颗粒上形成水。 这一主题对于理解水的输送及其在行星中的结合非常重要。

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.