Electron Irradiation of Carbon Disulfide-Oxygen Ices: Toward the Formation of Sulfur-Bearing Molecules in Interstellar Ices

Abstract

The formation of sulfur-bearing molecules in interstellar ices was investigated during the irradiation of carbon disulfide (CS 2 )-oxygen (O 2 ) ices with energetic electrons at 12 K. The irradiation-induced chemical processing of these ices was monitored online and in situ via Fourier transform infrared spectroscopy to probe the newly formed products quantitatively. The sulfur-bearing molecules produced during the irradiation were sulfur dioxide (SO 2 ), sulfur trioxide (SO 3 ), and carbonyl sulfide (OCS). Formations of carbon dioxide (CO 2 ), carbon monoxide (CO), and ozone (O 3 ) were observed as well. To fit the temporal evolution of the newly formed products and to elucidate the underlying reaction pathways, kinetic reaction schemes were developed and numerical sets of rate constants were derived. Our studies suggest that carbon disulfide (CS 2 ) can be easily transformed to carbonyl sulfide (OCS) via reactions with suprathermal atomic oxygen (O), which can be released from oxygen-containing precursors such as water (H 2 O), carbon dioxide (CO 2 ), and/or methanol (CH 3 OH) upon interaction with ionizing radiation. This investigation corroborates that carbonyl sulfide (OCS) and sulfur dioxide (SO 2 ) are the dominant sulfur-bearing molecules in interstellar ices.

Organosulfur Compounds Formed by Sulfur Ion Bombardment of Astrophysical Ice Analogs: Implications for Moons, Comets, and Kuiper Belt Objects

“…, 2016Van Dishoeck 2014;Schlemmer et al 2015;Ö b e r g 2016;F r e s n e a ue ta l .2017). Sulfur chemistry in laboratory ice experiments has been mainly studied in two ways, (i) irradiation by nonsulfurous particles of sulfur-bearing ices (e.g., via UV photons (Chen et al 2014), electrons (Maity & Kaiser 2013;Mahjoub et al 2017;P o s t o ne ta l .2018)), or protons (Moore 1984;Moore et al 2007;F e r r a n t ee ta l .2008; Strazzulla et al 2009;Garozzo et al 2010;Loeffler et al 2011) and (ii) irradiation by S projectiles of non-sulfur-bearing ices (Strazzulla et al 2007(Strazzulla et al , 2009;D i n ge ta l .2013;L ve ta l .2013; Boduch et al 2016).U V photons can induce the formation of more complex sulfur-bearing 1 molecules (OCS or CS 2 ) inside initial H 2 S ices (Chen et al 2014). Also, electrons can trigger the formation of complex S molecules (small sulfur allotropes or even complex organosulfur compounds within H 2 S-bearing ices) ( Mahjoub et al 2017).…”

Single and double addition of oxygen atoms to propyne on surfaces at low temperatures

“…Here we distinguish thermal surface chemistry, where reactions occur on the surface without the input of additional energy, with activated chemistry, where reactions are initiated and molecules subsequently processed, by external agents such as cosmic rays. 16 To our knowledge, despite propyne being repeatedly detected in the ISM, the reactivity of propyne on cold surfaces, such as those of dust grains, has not yet been investigated. In contrast, the chemistry of methanol on interstellar surfaces has been extensively studied.…”

Electron irradiation of carbon dioxide-carbon disulphide ice analog and its implication on the identification of carbon disulphide on Moon

“…9 Vibrational features of CS 2 were observed at 2146 cm −1 , 1511 cm −1 and 1460 cm −1 and in good agreement with other experimental data reported. 7 In addition, to the bands corresponding to CO 2 and CS 2 a prominent band at with peak center at 1039 cm −1 was also observed where this could be from the S-O vibration that can arise from the complex CS 2 -CO 2 .…”