Photochemistry and radiation chemistry of interstellar ices lead to the synthesis of prebiotic molecules which may be delivered to planets by meteorites and/or comets.

Principles that predict reactions or properties of materials define the discipline of chemistry. In this work we derive chemical rules, based on atomic distances and chemical bond character, which predict topological materials in compounds that feature the structural motif of a square-net. Using these rules we identify over 300 potential new topological materials. We show that simple chemical heuristics can be a powerful tool to 1 arXiv:2002.04611v1 [cond-mat.mtrl-sci] 11 Feb 2020 characterize topological matter. In contrast to previous database-driven materials categorization our approach allows us to identify candidates that are alloys, solid-solutions, or compounds with statistical vacancies. While previous material searches relied on density functional theory, our approach is not limited by this method and could also be used to discover magnetic and statistically-disordered topological semimetals.

We report the identification of methoxymethanol (CH 3 OCH 2 OH) as a photochemistry product of condensed methanol (CH 3 OH) based on temperature-programmed desorption studies conducted following photon irradiation at energies below the ionization threshold (9.8 eV) of condensed methanol. The first detection of methoxymethanol in the interstellar medium was reported in 2017 based on data from Bands 6 and 7 from the Atacama Large Millimeter/submillimeter Array (ALMA). The cosmic synthesis of "complex" organic molecules such as methyl formate (HCOOCH 3 ), dimethyl ether (CH 3 OCH 3 ), acetic acid (CH 3 COOH), ethylene glycol (HOCH 2 CH 2 OH), and glycolaldehyde (HOCH 2 CHO) has been attributed to UV photolysis of condensed methanol found in interstellar ices. Experiments conducted in 1995 demonstrated that electron-induced radiolysis of methanol cosmic ice analogues yields methoxymethanol. In three recent publications (2016, 2017, and 2018), methoxymethanol was considered as a potential tracer for reactions induced by secondary electrons resulting from the interaction of cosmic rays with interstellar ices. However, the results presented in this study suggest that methoxymethanol can be formed from both radiation chemistry and photochemistry of condensed methanol.

While gas-phase reactions and surface reactions on bare carbonaceous or siliceous dust grains contribute to cosmic chemistry, the energetic processing of cosmic ices via photochemistry and radiation chemistry is thought to be the dominant mechanism for the cosmic synthesis of prebiotic molecules. Because most previous laboratory astrochemical studies have used light sources that produce >10 eV photons and are, therefore, capable of ionizing cosmic ice analogs, discerning the role of photochemistry vs. radiation chemistry in astrochemistry is challenging. By using a source whose photon energy does not exceed 8 eV, we have studied ammonia and methanol cosmic ice reactions attributable solely to photochemistry. We compare these results to those obtained in the same ultrahigh vacuum chamber with 1 keV electrons which instead initiate radiation chemistry in cosmic ice analogs.