Hydroxylamine in astrophysical ices: Infrared spectra and cosmic-ray-induced radiolytic chemistry

¹ Instituto de Estructura de la Materia, IEM-CSIC, Calle Serrano 121, 28006 Madrid, Spain
² Instituto de Fisica Fundamental, IFF-CSIC, Calle Serrano 121, 28006 Madrid, Spain
³ HUN-REN Institute for Nuclear Research (Atomki), Bem Tér 18/C, Debrecen 4026, Hungary
⁴ Centro de Astrobiología (CAB), CSIC-INTA, Carretera de Ajalvir Km. 4, Torrejón de Ardoz, 28850 Madrid, Spain
⁵ Institute of Chemistry, University of Debrecen, Egyetem Tér 1, Debrecen 4032, Hungary
⁶ Doctoral School of Chemistry, University of Debrecen, Egyetem Tér 1, Debrecen 4032, Hungary
⁷ Centre for Interstellar Catalysis (InterCat), Department of Physics and Astronomy, Aarhus University, Aarhus 8000, Denmark

^★ Corresponding author; belen.mate@csic.es

Received: 5 December 2024
Accepted: 28 January 2025

Abstract

Context. Gas-phase hydroxylamine (NH₂OH) has recently been detected within dense clouds in the interstellar medium. However, it is also likely present within interstellar ices, as well as on the icy surfaces of outer Solar System bodies, where it may react to form more complex prebiotic molecules such as amino acids.

Aims. In this work, we aim to provide infrared spectra of NH₂OH in astrophysical ice analogues that will help in the search for this molecule in various astrophysical environments. Furthermore, we aim to provide quantitative information on the stability of NH₂OH upon exposure to ionising radiation analogous to cosmic rays, as well as on the ensuing chemistry and potential formation of complex prebiotic molecules.

Methods. Ices composed of NH₂ OH, H₂O, and CO were prepared by vapour deposition, and infrared spectra were acquired between 4000–500 cm⁻¹ (2.5–20 µm) prior to and during irradiation using 15 keV protons.

Results. Our spectroscopic characterisations determine that NH₂OH ices deposited at 10–20 K adopt an amorphous structure, which begins to crystallise upon warming to temperatures greater than 150 K. In interstellar ice analogues, the most prominent infrared absorption band of NH₂OH is that at about 1188 cm⁻¹, which may be a good candidate to use in searches for this species in icy space environments. Calculated effective destruction cross-sections and G-values for the NH₂ OH-rich ices studied show that NH₂OH is rapidly destroyed upon exposure to ionising radiation (more rapidly than a number of previously studied organic molecules) and that this destruction is slightly enhanced when it is mixed with other icy species. The irradiation of a NH₂OH:H₂O:CO ternary ice mixture leads to a rich chemistry that includes the formation of simple inorganic molecules such as NH₃, CO₂, OCN⁻, and H₂O₂, as well as ammonium salts and, possibly, complex organic molecules relevant to life such as formamide, formic acid, urea, and glycine.