VUV spectroscopy of an electron irradiated benzene : carbon dioxide interstellar ice analogue

Abstract

We present the first vacuum ultraviolet spectroscopic study of an interstellar ice analogue of a benzene (C6H6) : carbon dioxide (CO2) (1 : 100) mixture which has been energetically processed with 1 keV electrons.

Residue from vacuum ultraviolet irradiation of benzene ices: Insights into the physical structure of astrophysical dust

“…The VUV spectrum of benzene ice formed at 4 K is shown in Figure 1(a) and the spectral signatures observed were found to be in good agreement with those previously reported in literature (Dawes, Pascual et al 2017, James, Jones et al 2019. However, since the purpose of the experiment was to understand the physical structure of aromatic residue, which requires a large amount of residue after irradiation, a very thick ice had to be prepared before irradiation at 4 K, thus the most intense absorption bands of benzene in the 140 nm -220 nm were saturated but the rest of the characteristic bands of benzene ice that appear at 240 nm -275 nm were clearly seen.…”

“…Even in the irradiated mixtures of benzene and carbon dioxide ices, benzene derivatives were reported (Fig 1(d)) (James, Jones et al 2019).…”

“…[1] Shows the VUV spectra of (a) pure benzene ice deposited at 4 K on a LiF window, (b) of irradiated benzene ice and as a function of temperature until 300 K, (c) the residue compared with styrene ice and (d) the residue at 300 K in comparison with the residue spectra at 200 K reported by James et al (James , Jones et al 2019).…”

“…Many laboratory experiments have been carried out to understand the formation of aromatic molecules and also their dissociation both in pure (Callahan, Gerakines et al 2013 and references therein) and in mixtures of ices (James, Jones et al 2019 and references therein). While irradiating a pure benzene ice using keV protons the most intense infrared (IR) band of benzene was found to grow in intensity which was attributed to the synthesis of an aromatic residue (Strazzulla and Baratta 1991).…”

Mid-IR and VUV spectroscopic characterisation of thermally processed and electron irradiated CO2 astrophysical ice analogues

“…Although perhaps less popular than infrared spectroscopy, electronic spectroscopy has also been used in astrochemical studies of CO2 ice analogues (e.g., Mason et al 2006, Pavithraa et al 2019, James et al 2019, James et al 2020. Between 120 nm (10.3 eV) and 180 nm (6.9 eV), CO2 ice presents two broad absorption bands centred about 125 nm (9.9 eV) and 141 nm (8.8 eV) corresponding to the 1 Πg ← 1 Σg + and the 1 Δu ← 1 Σg + transitions, respectively.…”