Laboratory surface astrochemistry experiments

Icy Grain Mantle Surface Astrochemistry of MgNC: The Emergence of Metal Ion Catalysis Studied via Model Ice Cluster Calculations

One of a small number of known magnesium-containing astromolecules, magnesium isocyanide (MgNC) was first detected in 1986. MgNC is an intriguing reactant to consider: it is an open-shell radical in which its metal atom forms a bond with CN that is a mixture of ionic and covalent character. While its gas phase astrochemistry has received prior attention, the grain surface chemistry of MgNC has never been studied. Because of its ionic character, MgNC is found to interact far more strongly with an ice surface than molecules with a greater degree of covalency. As a radical, it may react with closed-shell molecules deposited from the gas phase. In this work, cluster calculations treated with density functional theory and correlation consistent basis sets were used to model the deposition of MgNC on clusters containing 17 and 24 water molecules, which were then allowed to react with acetylene (HCCH) and hydrogen cyanide (HCN) as well as with H atoms. The addition of H to MgNC-nH₂O yields hydromagnesium isocyanide (HMgNC), a known astromolecule that may be ejected into the gas phase. HCCH and HCN bind to MgNC-nH₂O to form intermediate radical compounds that may then also react with H atoms. There is enough reaction energy from H addition to eject fragments of the intermediates into the gas phase: the vinyl radical (C₂H₃) for HCCH and the methaniminyl radical (H₂CN) for HCN. That leaves MgNC-nH₂O to perform further catalytic activity. Alternatively, various hydrogenated divalent Mg compounds may also be stabilized and frozen into the ice or potentially ejected into the gas phase. Benchmark coupled cluster theory calculations in limited systems were used to characterize the submerged reaction barriers present when HCCH or HCN add to MgNC in the gas phase.

Highly Stable and Reactive Platinum Single Atoms on Oxygen Plasma-Functionalized CeO2 Surfaces: Nanostructuring and Peroxo Effects

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non-trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre-treatment of the ceria (CeO2 ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well-defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O2 2- ) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites.

Impact of oxygen chemistry on model interstellar grain surfaces

Temperature-programmed desorption (TPD) and reflection–absorption infrared spectroscopy (RAIRS) are used to probe the effect of atomic and molecular oxygen (O and O₂) beams on amorphous silica (aSiO₂) and water (H₂O) surfaces (porous-amorphous solid water; p-ASW, compact amorphous solid water; c-ASW, and crystalline solid water; CSW).

Surface heterogeneity and inhomogeneous broadening of vibrational line profiles

The surface heterogeneity of amorphous silica (aSiO₂) has been probed using coverage dependent temperature programmed desorption (TPD) of a simple probe molecule, carbon monoxide (CO), and is used to explain the inhomogeneous broadening of the CO stretching vibration in the infrared.

Spontaneous polarization of solid CO on water ices and some astrophysical implications

Reflection absorption infrared spectroscopy (RAIRS) is used to show that when 20 monolayer (ML) films of solid CO are laid down on solid water substrates at 20 to 24 K, the films polarize spontaneously.

Peeling the astronomical onion

This work presents a study of water mobility on interstellar dust grain analogues at temperatures as low as 18 K. The work indicates that water forms pure domains rather than covering the entire grain, thereby leaving bare dust grain surfaces available on which other molecules can adsorb as well as themselves providing surfaces for further adsorption from the interstellar gas.

Spontaneous electric fields in solid carbon monoxide

Reflection–absorption infrared spectroscopy (RAIRS) is shown to provide a means of observing the spontelectric phase of matter, the defining characteristic of which is the occurrence of a spontaneous and powerful static electric field within a film of material.

Spontaneously electrical solids in a new light

Reflection–absorption infrared spectroscopy (RAIRS) of nitrous oxide (N₂O) thin films is shown to provide an independent means of observing the spontelectric state; the first new structural phase of matter, with unique electrical properties, to have emerged in decades.