Efficient surface formation route of interstellar hydroxylamine through NO hydrogenation. II. The multilayer regime in interstellar relevant ices

Abstract

Hydroxylamine (NH 2 OH) is one of the potential precursors of complex pre-biotic species in space. Here, we present a detailed experimental study of hydroxylamine formation through nitric oxide (NO) surface hydrogenation for astronomically relevant conditions. The aim of this work is to investigate hydroxylamine formation efficiencies in polar (water-rich) and non-polar (carbon monoxiderich) interstellar ice analogues. A complex reaction network involving both final (N 2 O, NH 2 OH) and intermediate (HNO, NH 2 O · , etc.) products is discussed. The main conclusion is that hydroxylamine formation takes place via a fast and barrierless mechanism and it is found to be even more abundantly formed in a water-rich environment at lower temperatures. In parallel, we experimentally verify the non-formation of hydroxylamine upon UV photolysis of NO ice at cryogenic temperatures as well as the non-detection of NC-and NCO-bond bearing species after UV processing of NO in carbon monoxide-rich ices. Our results are implemented into an astrochemical reaction model, which shows that NH 2 OH is abundant in the solid phase under dark molecular cloud conditions. Once NH 2 OH desorbs from the ice grains, it becomes available to form more complex species (e.g., glycine and β-alanine) in gas phase reaction schemes.

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO2

“…The presence of HNO in the ice can be explained by the nature of the co-deposition experiments, where the continuous deposition of new molecules on the cold ice surface causes some of the formed HNO to get trapped in the ice matrix, where it is not further converted into NH 2 OH as shown in ref. [11][12][13]. The formation of species not previously detected during the hydrogenation of pure NO 2 or pure CO indicates that the interaction of the two reaction pathways leads toward a higher degree of chemical complexity in the ice.…”

“…In particular, spectrum (a) confirms the formation of formaldehyde after hydrogenation of 13 CO ice; [25][26][27] spectrum (b) clearly shows all the carbon monoxide isotopologues, as well as the NO 2 monomer, N 2 O 3 and N 2 O 4 . The strong NO 2 feature seen in spectrum (b) at 1612 cm À1 almost disappears in spectrum (c) where new features due to 13 CO 2 , HO 13 CO, H 13 COOH, HNO, and NH 2 OH show up. The presence of HNO in the ice can be explained by the nature of the co-deposition experiments, where the continuous deposition of new molecules on the cold ice surface causes some of the formed HNO to get trapped in the ice matrix, where it is not further converted into NH 2 OH as shown in ref.…”

“…Fig. 3 shows the co-deposition spectrum of 13 CO + H = 1 : 1.5 at 13.5 K (a) compared to the co-deposition of NO 2 + 13 CO = 1 : 50 (b) and the co-deposition of NO 2 + 13 CO + H = 1 : 50 : 10 (c), both at 15 K. All these experiments have the same H-atom fluence (1.5 Â 10 16 atoms cm À2 ) as well as the same NO 2 and 13 CO deposition rates (0.05 and 2.5 L min À1 ) when deposited together. Therefore, a comparison of these spectra gives a qualitative picture of the destruction of solid NO 2 and allows for the identification of new species formed through the hydrogenation of the ice.…”

“…3 are due to the hydrogenation of NO 2 : i.e., the hydrogenation products of solid 13 CO (H 2 13 CO and 13 CH 3 OH) are under the detection limit. HO 13 CO, 13 CO 2 , and H 13 COOH are all products of the reaction OH + 13 CO as is discussed in Section 4.…”

“…Here, NO 2 + N is also studied in an apolar astrochemically relevant CO ice at 15 K. Fig. 7 shows the spectrum of a 13 Table 2). …”