The uptake and potential reactivity of metal atoms on water ice can be an important process in planetary atmospheres and on icy bodies in the interplanetary and interstellar medium. For instance, metal atom uptake affects the gas-phase chemistry of the Earth's mesosphere, and has been proposed to influence the agglomeration of matter into planets in protoplanetary disks. In this study the fate of Mg and K atoms incorporated into water-ice films, prepared under ultra-high vacuum conditions at temperatures of 110–140 K, was investigated. Temperature-programmed desorption experiments reveal that Mg- and K-containing species do not co-desorb when the ice sublimates, demonstrating that uptake on ice particles causes irreversible removal of the metals from the gas phase. This implies that uptake on ice particles in terrestrial polar mesospheric clouds accelerates the formation of large meteoric smoke particles (≥1 nm radius above 80 km) following sublimation of the ice. Energetic sputtering of metal-dosed ice layers by 500 eV Ar+ and Kr+ ions shows that whereas K reacts on (or within) the ice surface to form KOH, adsorbed Mg atoms are chemically inert. These experimental results are consistent with electronic structure calculations of the metals bound to an ice surface, where theoretical adsorption energies on ice are calculated to be −68 kJ mol−1 for K, −91 kJ mol−1 for Mg, and −306 kJ mol−1 for Fe. K can also insert into a surface H2O to produce KOH and a dangling H atom, in a reaction that is slightly exothermic.
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机译：在行星大气以及行星际和星际介质中的冰体上，水冰上金属原子的吸收和潜在的反应性可能是一个重要过程。例如，金属原子的吸收会影响地球中层大气的气相化学性质，因此已提出影响金属原子在原行星盘中的团聚。在这项研究中，研究了在超高真空条件下在110–140 K的温度下制备的掺入水冰膜中的Mg和K原子的命运。程序升温解吸实验表明，当冰升华时，含Mg和K的物质不会同时解吸，这表明冰粒上的吸收会导致不可逆地从气相中去除金属。这意味着，在陆地升华后，陆地极地中层云中的冰粒被吸收加速了大的陨石烟粒（半径大于80 km大于1 nm）的形成。用500 eV Ar +和Kr +离子对金属配料的冰层进行高能溅射表明，尽管K在冰表面上（或内部）反应形成KOH，但吸附的Mg原子是化学惰性的。这些实验结果与结合到冰表面的金属的电子结构计算相符，其中理论上在冰上的吸附能被计算为K为-68 kJ mol-1，Mg为-91 kJ mol-1和-306 kJ铁的mol-1。在轻微放热的反应中，K还可插入表面H2O中以产生KOH和悬挂的H原子。
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