Ion irradiation of N2O ices and NO2:N2O4 ice mixtures: first steps to understand the evolution of molecules with the N-O bond in space

Abstract

Astronomical observations towards star-forming regions have revealed the presence of molecules with the N-O bond such as NO, N<SUB>2</SUB>O, and HNO. These species are considered potential precursors of prebiotic molecules. Thus, understanding nitrogen and oxygen chemistry may help us to better understand the origin and evolution of prebiotic molecules in space. However, species with the N-O bond are poorly studied and laboratory works on the effects induced on them by solar wind and galactic cosmic rays are still scarce. For this, we wanted to study the effects of ion bombardment on molecules with the N-O bond. We focus here on N<SUB>2</SUB>O ices and NO<SUB>2</SUB>:N<SUB>2</SUB>O<SUB>4</SUB> = 1:1 ice mixtures (at 16 and 50/60 K) irradiated with 200 keV protons. Infrared transmission spectroscopy (8000-500 cm<SUP>-1</SUP>; 1.25-20 μm) was used to analyse the samples. Irradiation of N<SUB>2</SUB>O ices and NO<SUB>2</SUB>:N<SUB>2</SUB>O<SUB>4</SUB> ice mixtures produces comparable effects independent of the irradiation temperature, NO being the main product. Moreover, we show that the maximum amount of N<SUB>2</SUB>O and N<SUB>2</SUB>O<SUB>4</SUB> destroyed by irradiation, at the highest dose reached in our experiments, is equal to about 98 and 70 {{ per cent}}, respectively. The dose range covered in the experiments has been compared with the astrophysical time-scale of surface processing in space, showing that irradiation of N<SUB>2</SUB>O and NO<SUB>2</SUB>:N<SUB>2</SUB>O<SUB>4</SUB> mixtures can produce, within 10<SUP>5</SUP>-10<SUP>8</SUP> yr, amounts of solid NO ice detectable towards star-forming regions by the James Webb Space Telescope.