VUV photoabsorption of thermally processed carbon disulfide and ammonia ice mixtures – Implications for icy objects in the solar system

[Display omitted] •VUV spectra of pure CS2 ice in the 110 – 350 nm region in astrochemical icy condition.•Broader VUV absorption of ∼100 nm for pure CS2 ice observed for the first time in a small molecule (164 – 259 nm region).•VUV spectra of CS2-NH3 ice layers and mixtures in astrochemical icy condition.•Temperature dependent study of the pure CS2, CS2-NH3 layers, CS2-NH3 mixtures from 10 K to higher temperature, 140 K – 250 K.•Presence of a CS2-NH3 complex or residue at higher temperatures (140 K – 250 K). Many icy bodies in the solar system have been found to contain a rich mixture of simple molecules on their surfaces. Similarly, comets are now known to be a reservoir of molecules ranging from water to amides. The processing of planetary/cometary ices leads to the synthesis of more complex molecules some of which may be the harbingers of life. Carbon disulphide (CS2) and ammonia (NH3) are known to be present on many icy satellites and comets. Reactions involving CS2 and NH3 may lead to the formation of larger molecules that are stable under space conditions. In this paper we present temperature dependent VUV spectra of pure CS2 in the ice phase, and of CS2 and NH3 ices deposited as (i) layered, and (ii) mixed ices at 10 K and warmed to higher temperatures until their sublimation. Pure CS2 ice is found to have a broad absorption in the VUV region, which is unique for a small molecule in the ice phase. In layered and mixed ices, the molecules tend to affect the phase change and sublimation temperature of each other and also leave behind a form of CS2−NH3 complex after thermal annealing. This study of CS2-NH3 ice systems in layered and mixed configurations would support the detection of these species/complexes in mixed molecular ices analogous to that on planetary and cometary surfaces.