Cosmic-ray-induced chemical processes in CH₃OH, CH₃NH₂, and CH₃OH:CH₃NH₂ ices

Conventional and novel IR spectroscopic analysis with VIZSLA

¹ Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, 1518 Budapest, Hungary
² Hevesy György PhD School of Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, 1518 Budapest, Hungary
³ MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, 1518 Budapest, Hungary
⁴ Wigner Research Centre for Physics, PO Box 49, 1525 Budapest, Hungary
⁵ Centre for Astrophysics and Space Science, ELTE Eötvös Loránd University, PO Box 32, 1518 Budapest, Hungary

^★ Corresponding author; gyorgy.tarczay@ttk.elte.hu

Received: 8 September 2024
Accepted: 13 November 2024

Abstract

Aims. Icy mantles on interstellar dust grains are considered key contributors to the chemical complexity of the interstellar medium (ISM). Gas-phase molecules in the ISM can adsorb onto these icy surfaces, where chemical reactions can be induced by ultraviolet (UV) or cosmic ray (CR) irradiation. The resulting molecules can subsequently desorb, thereby altering the composition of the gas phase in the ISM. Therefore, studying astrochemically relevant reactions within ices is essential for advancing our understanding of astrochemistry.

Methods. We conducted experiments with pure methanol (CH₃OH), pure methylamine (CH₃NH₂), and CH₃OH:CH₃NH₂ ices. To simulate CR effects, ices were irradiated with 5 keV electrons. We integrated the advantages of ice experiments and noble gas matrix experiments by performing two distinct investigations on each sample. During temperature-programmed desorption (TPD), chemical changes in the ice samples were monitored using Fourier transform infrared (FTIR) spectroscopy. In addition, the desorbing molecules were trapped in an Ar matrix through a following experiment. This TPD-matrix-isolation (TPD-MI) redeposition process enabled FTIR spectroscopic identification of the desorbed species.

Results. The results obtained from experiments with CH₃OH and CH₃NH₂ ices are consistent with previous studies. Additionally, the TPD-MI redeposition process enabled the identification of several species previously not detected clearly and directly in pure CH₃OH or CH₃NH₂ ices, including molecules such as HCOOH, HCN, and CH₂CHNH. Our experiments with CH₃OH:CH₃NH₂ mixtures revealed the formation of several nitrogen- and oxygen-containing organic species (CH₃NHCH₂OH, NH₂CH₂OH, NH₂CH₂CH₂OH, and HNCO), which are potential precursors to prebiotic molecules in the ISM. Therefore, these experiments provide valuable insights into the chemical evolution in space.