Nitrogen oxides and carbon chain oxides formed after ion irradiation of CO:N₂ice mixtures

Abstract

Context. High CO depletion as well as depletion of N-bearing species is observed in dense pre-stellar cores. It is generally accepted that depleted species freeze out onto dust grains to form icy mantles and that these ices suffer energetic processing due to cosmic ion irradiation and ion-induced UV photons. Aims. The aim of this work is to study the chemical and structural effects induced by ion irradiation on different CO:N 2 mixtures at low temperature (16 K) to simulate the effects of cosmic ion irradiation of icy mantles. Methods. Different CO:N 2 mixtures and pure CO and pure N 2 were irradiated with 200 keV H + at 16 K. Infrared transmittance spectra of the samples were obtained in situ before and after irradiation. The samples were warmed up and spectra were taken at different temperatures. The residues left over on the substrate at room temperature were analysed ex situ by micro Raman spectroscopy. Results. Several new absorption features are present in the infrared spectra after irradiation, indicating that new species are formed. The most abundant are nitrogen oxides (such as NO, NO 2 and N 2 O), carbon chain oxides (such as C 2 O, C 3 O and C 3 O 2 ), carbon chains (such as C 3 and C 6 ), O 3 and N 3 . A refractory residue is also formed after ion irradiation and is clearly detected by Raman spectroscopy. Conclusions. We suggest that carbon chains and nitrogen oxides observed in the gas phase towards star-forming regions are formed in the solid phase after cosmic ion irradiation of icy grain mantles and are released into the gas phase after desorption of grain mantles. We expect that the Atacama Large Millimeter/submillimeter Array (ALMA), thanks to its high sensitivity and resolution, will increase the number of nitrogen oxides and carbon chain oxides detected towards star-forming regions.

Chemistry induced by energetic ions in water ice mixed with molecular nitrogen and oxygen

“…These doses are sufficient to alter the chemical composition. Based on the present results, NO, NO 2 and N 2 O are formed (note that nitrogen oxides are also formed after ion bombardment of mixtures containing nitrogen and carbon monoxide, Sicilia et al 2012). We suggest here that the measurement of molecular ratios NO/NO 2 and NO/N 2 O in the ice and/or in the tenuous atmospheres of those objects are useful to confirm the presence of nitrogen and reveal if oxygen is present as well.…”

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

“…However, reactions (10) and (11) are potentially still limited by the interstellar low abundance of the parent species. Finally, nitrogen-bearing acids, like nitrous acid and nitric acid, can be formed through surface reactions (7) and (8). Although the formation of these acids was not verified here, their interstellar relevance should not be excluded.…”

“…When carbon-bearing species are present in the ice that are irradiated with a mixture containing N 2 , OCN À is also formed. 7,8 Laboratory studies of non-energetic surface processing showed that, for instance, ammonia (NH 3 ), hydroxylamine (NH 2 OH), nitrogen dioxide (NO 2 ), dinitrogen trioxide (N 2 O 3 ), nitrous acid (HNO 2 ), and nitric acid (HNO 3 ) are efficiently formed at low temperatures through hydrogenation of N-atoms, NO + H, NO + O 2 , NO + NO 2 , NO + OH, and NO 2 + OH reactions, respectively. [9][10][11][12][13][14][15][16] In the accompanying paper, hereafter referred to as Part I, 17 we investigate the oxygenation of solid NO (NO + O/O 2 /O 3 ) at a Division of Geological and Planetary Sciences, California Institute of Technology,…”

Solid CO2in low-mass young stellar objects

“…This is because CO 2 is not in a pure ice but is mixed with other species, such as carbon chain oxides formed after ion irradiation (see e.g. Palumbo et al 2008), and is trapped in a refractory residue also formed at low temperature after ion irradiation (Sicilia et al 2012). The experiment shown in the top-right panel of Fig.…”