Vacuum Ultraviolet Photon-Stimulated Oxidation of Buried Ice: Graphite Grain Interfaces

Abstract

The vacuum ultraviolet (VUV) synthesis of CO and CO 2 on ice-coated graphite and isotopic labeled 13 C graphite has been examined for temperatures between 40 and 120 K. The results show that CO and CO 2 can be formed at the buried ice:graphite interface with Lyα photon irradiation via thereaction of radicals (O and OH) produced by direct photodissociation and the dissociative electron attachment of the interfacial water molecules. The synthesized CO and CO 2 molecules can desorb in hot photon-dominated regions and arelost to space when ice coated carbonaceous dust grains cycle within the protoplanetary disks. Thus, the nonthermal formation of CO and CO 2 at the buried ice:grain interface by VUV photons may help regulate the carbon inventory during the early stage of planet formation. This may contribute to the carbon deficits in our solar systemand suggests that a universal carbon deficit gradient may be expected within astrophysical bodies surrounding center stars.

Electron-molecule chemistry and charging processes on organic ices and Titan’s icy aerosol surrogates

“…These oxygen atoms or hydroxyl groups can be released during X-ray, electron and vacuum ultraviolet photon irradiation and contribute to oxidation of the tholin-like residue directly at the surface. The total cross section for producing CO and CO 2 from VUV irradiated water (43 nm thickness) covered graphite grains is $1.2 Â 10 À18 -cm 2 (Shi et al, 2015). Assuming the same substrate oxygen density and reaction probability with the HCN overlayer, the low intrinsic oxygen on the graphite only contributes a small fraction of the oxygen incorporation observed in the polymer residue.…”

A Geoscientific Review on CO and CO2 Ices in the Outer Solar System

“…On the other hand, CO 2 grains produced from CO + O reactions and CO radiolysis can (if heated) increase this ratio due to the higher volatility of CO [59]. Lab experiments demonstrate that radiolysis of H 2 O ice and C-rich substrates driven by charged particle irradiation can generate CO 2 [43,[67][68][69][70][71]. The CO 2 produced by bombardment of ions and UV photons in simple ices effects such processing ranges, from ion sputtering, physical modification of the crystalline structure, and induction of non-thermal chemical reactions resulting in the refractory of organic residues [72][73][74][75].…”

“…Since UV radiation and cosmic rays are the potential culprits for the irradiation mechanisms on CO 2 , the low-albedo regions may contain C-bearing molecular species, such as CH 4 . From experimental work, radiation of water-covered graphene (or graphene oxides) produces CO 2 during these processes, including UV and various radiation sources [70].…”

VUV Spectral Irradiance Measurements in H2/He/Ar Microwave Plasmas and Comparison with Solar Data

“…Accounting for the monochromatic method, it is evident that the integrated photon flux is relatively higher compared to the polychromatic flux at Lyα (see Es-sebbar et al 2015). Based on our previous studies (Bénilan et al 2011), Orlando et al (Dawley et al 2014;Shi et al 2015) were the first to use microwave plasmas in the ternary mixture of 2% H 2 /18% Ar/He mixture for irradiation experiments to mimic reactions that may occur in 1.01% H 2 /49% Ar/He 9.4 6.24 Act 3…”

“…Spectral irradiance and photon flux of vacuum ultraviolet sources are crucial parameters in all photochemistry processes, astrophysical studies, and laboratory simulations of planetary atmospheres (Baratta et al 2002;Cottin et al 2003;Romanzin et al 2010;Chen et al 2014;Cruz-Diaz et al 2014;Shi et al 2015). Hydrogen Lyα sources (Lyα at 121.6 nm∼10.2 eV or the H I line) simulating the solar spectrum have been widely used in laboratory experiments.…”