Abstract
Many experimental parameters determine the chemical and physical properties of interstellar ice analogues, each of which may influence the molecular synthesis that occurs in such ices. In part 1, James et al., RSC Adv., 2020, 10, 37517, we demonstrated the effects that the stoichiometric mixing ratio had on the chemical and physical properties of CO2 : NH3 mixtures and the impact on molecular synthesis induced by thermal processing. Here, in part 2, we extend this to include 1 keV electron irradiation at 20 K of several stoichiometric mixing ratios of CO2 : NH3 ices followed by thermal processing. We demonstrate that not all stoichiometric mixing ratios of CO2 : NH3 ice form the same products. Not only did the 4 : 1 ratio form a different residue after thermal processing, but O3 was observed after electron irradiation at 20 K, which was not observed in the other ratios. For the other ratios, the residue formed from a thermal reaction similar to the work shown in Part 1. However, conversion of ammonium carbamate to carbamic acid was hindered due to electron irradiation at 20 K. Our results demonstrate the need to systematically investigate stoichiometric mixing ratios to better characterise the chemical and physical properties of interstellar ice analogues to further our understanding of the routes of molecular synthesis under different astrochemical conditions.
Highlights
Our results demonstrate the need to systematically investigate stoichiometric mixing ratios to better characterise the chemical and physical properties of interstellar ice analogues to further our understanding of the routes of molecular synthesis under different astrochemical conditions
Interstellar ice analogue experiments play an important role in understanding molecular synthesis in the interstellar medium (ISM), and systematic investigations into the experimental parameters can provide a wealth of information
We systematically investigated the effect of the stoichiometric mixing ratio on 1 keV e-irradiated CO2 : NH3 ices and subsequent thermal processing using mid-IR and VUV spectroscopy
Summary
Interstellar ice analogue experiments play an important role in understanding molecular synthesis in the interstellar medium (ISM), and systematic investigations into the experimental parameters can provide a wealth of information. The NH3-rich CO2 : NH3 mixtures (e.g. 1 : 3, 1 : 10) formed higher amounts of residue material where more NH3 crystallite grain boundaries existed, suggesting that structural diffusion of reactants may be linked to enhanced reactivity of this system. In this follow-up paper, we extend our study of the discrete experimental parameter of stoichiometric mixing ratios of CO2 : NH3 ices to include 1 keV electron irradiation at 20 K followed by thermal processing. This paper presents the rst study dedicated to investigating the non-thermal processing of different stoichiometric mixing ratios of CO2 : NH3 ices
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