A new multi-beam apparatus for the study of surface chemistry routes to formation of complex organic molecules in space

Binding energies of ethanol and ethylamine on interstellar water ices: synergy between theory and experiments

Experimental and computational chemistry are two disciplines used to conduct research in astrochemistry, providing essential reference data for both astronomical observations and modeling. These approaches not only mutually support each other, but also serve as complementary tools to overcome their respective limitations. Leveraging on such synergy, we characterized the binding energies (BEs) of ethanol (CH3CH2OH) and ethylamine (CH3CH2NH2), two interstellar complex organic molecules (iCOMs), on crystalline and amorphous water ices through density functional theory (DFT) calculations and temperature-programmed desorption (TPD) experiments. Experimentally, CH3CH2OH and CH3CH2NH2 behave similarly, in which desorption temperatures are higher on the water ices than on a bare gold surface. Computed cohesive energies of pure ethanol and ethylamine bulk structures allow describing of the BEs of the pure species deposited on the gold surface, as extracted from the TPD curve analyses. The BEs of submonolayer coverages of CH3CH2OH and CH3CH2NH2 on the water ices cannot be directly extracted from TPD due to their co-desorption with water, but they are computed through DFT calculations, and found to be greater than the cohesive energy of water. The behaviour of CH3CH2OH and CH3CH2NH2 is different when depositing adsorbate multilayers on the amorphous ice, in that, according to their computed cohesive energies, ethylamine layers present weaker interactions compared to ethanol and water. Finally, from the computed BEs of ethanol, ethylamine and water, we can infer that the snow-lines of these three species in protoplanetary disks will be situated at different distances from the central star. It appears that a fraction of ethanol and ethylamine is already frozen on the grains in the water snow-lines, causing their incorporation in water-rich planetesimals.

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.

VIZSLA-Versatile Ice Zigzag Sublimation Setup for Laboratory Astrochemistry

In this article, a new multi-functional high-vacuum astrophysical ice setup, VIZSLA (Versatile Ice Zigzag Sublimation Setup for Laboratory Astrochemistry), is introduced. The instrument allows for the investigation of astrophysical processes both in a low-temperature para-H₂ matrix and in astrophysical analog ices. In the para-H₂ matrix, the reaction of astrochemical molecules with H atoms and H⁺ ions can be studied effectively. For the investigation of astrophysical analog ices, the setup is equipped with various irradiation and particle sources: an electron gun for modeling cosmic rays, an H atom beam source, a microwave H atom lamp for generating H Lyman-α radiation, and a tunable (213-2800 nm) laser source. For analysis, an FT-IR (and a UV-visible) spectrometer and a quadrupole mass analyzer are available. The setup has two cryostats, offering novel features for analysis. Upon the so-called temperature-programmed desorption (TPD), the molecules, desorbing from the substrate of the first cryogenic head, can be mixed with Ar and can be deposited onto the substrate of the other cryogenic head. The efficiency of the redeposition was measured to be between 8% and 20% depending on the sample and the redeposition conditions. The well-resolved spectrum of the molecules isolated in an Ar matrix serves a unique opportunity to identify the desorbing products of a processed ice. Some examples are provided to show how the para-H₂ matrix experiments and the TPD-matrix-isolation recondensation experiments can help understand astrophysically important chemical processes at low temperatures. It is also discussed how these experiments can complement the studies carried out by using similar astrophysical ice setups.