Formation of Complex Organic and Prebiotic Molecules in H₂O:NH₃:CO₂ Ices at Temperatures Relevant to Hot Cores, Protostellar Envelopes, and Planet-Forming Disks

Abstract

Photochemistry in H 2 O:NH 3 :CO 2 cosmic ice analogues was studied at temperatures of 75, 120, and 150 K, relevant to hot cores and warmer regions in protostellar envelopes and planet-forming disks. A combination of two triggers of surface chemistry in cosmic ice analogues, heat and UV irradiation, compared to using either just heat or UV irradiation, leads to a larger variety and an increased production of complex organic molecules, including potential precursors of prebiotic molecules. In addition to complex organic molecules detected in previous studies of H 2 O:NH 3 :CO 2 ices, ammonium carbamate, carbamic acid, ammonium formate and formamide, we detected acetaldehyde, urea, and, tentatively, glycine, the simplest amino acid. Water ice hampers reactions at low temperature (75 K) but allows the parent molecules, CO 2 and NH 3 , to stay in the solid state and react at higher temperatures (120 and 150 K, above their desorption temperatures). The experiments were performed on the surface of KBr substrates and amorphous silicate grains, analogs of cosmic silicate dust. The production of complex molecules on the silicate surface is decreased compared to KBr. This result suggests that the larger surface area and/or surface properties of the silicate grains play a role in controlling the chemistry, preventing it taking place to the same extent as on the flat KBr substrate. This is further evidence of the fact that cosmic dust grains play an important role in the chemistry taking place on their surface.

Formation of CO2 Driven by Photochemistry of Water Ice Mixed with Carbon Grains

“…A possible influence of the relatively high base pressure in our experiments on the desorption efficiency at high temperatures can be questioned. In our recent study (Potapov et al 2022), we investigated the formation of molecules in H 2 O: NH 3 : CO 2 mixtures irradiated by UV at 120 and 150 K under the base pressure of 10 −10 mbar. One of the side results was that the amount of desorbed NH 3 and CO 2 reactants was only a few percent of the deposited amount; thus, the volatiles were mainly trapped in the ice matrix.…”

Formation of N–O–H bearing species in HNO3 and H2O icy samples by heavy-ion irradiation: an infrared spectroscopic study

“…Focusing on the H 2 O dissociation, both H and O radicals can undergo radicalradical reactions either to form H 3 O (1763.5 cm −1 ) [15] and H 2 O 2 at 1448.0 [48] and 2860 cm −1 [63]. H 2 O 2 can form HO 2 (3374.5 cm −1 ) [37]; loosing an H radical, HO 2 then can dissociate into O 2 , the latter can subsequently combine with a O radical to form O 3 [45]. Since O 2 is a homonuclear molecule, it does not exhibit a band in the IR spectrum.…”

Exploring Refractory Organics in Extraterrestrial Particles

“…Organic compounds, which are critical for life as we know it, such as ribose, amino acids, and nucleobases, have been detected in meteorites and comets (Cronin & Chang 1993;Elsila et al 2009;Cobb & Pudritz 2014;Altwegg et al 2016) and synthesized in laboratory experiments simulating the evolution of icy dust grains in the interstellar medium (ISM; Bernstein et al 2002;Muñoz Caro et al 2002;Nuevo et al 2006;Elsila et al 2007;Nuevo et al 2012;Meinert et al 2016;Oba et al 2016;Krasnokutski et al 2020) and circumstellar disks around young stars (Potapov et al 2022). Moreover, meteorites, comets, and IDPs contain refractory organic compounds (Cooper et al 2001;Matrajt et al 2004;Keller et al 2006;Rotundi et al 2008;Dartois et al 2013;Rotundi et al 2014;Goesmann et al 2015;Dartois et al 2018;Dionnet et al 2018).…”