Vacuum-Ultraviolet Photolysis of Methane at 3 K: Synthesis of Carbon Clusters up to C₂₀

Abstract

Samples of pure methane and of methane dispersed in solid neon at 3 K subjected to irradiation at wavelengths less than 165 nm with light from a synchrotron yielded varied products that were identified through their infrared absorption spectra, including CH3, C2H2, C2H3, C2H4, C2H6, C4H2, C4H4, C5H2, C8H2, CnH with n = 1-5, and carbon chains Cn with n = 3-20. The efficiency of photolysis of methane and the nature of the photoproducts depended on the concentration of methane and the wavelength selected for irradiation; an addition of H2 into solid neon enhanced the formation of long carbon chains.

VUV Photolysis of CH4–H2O mixture in methane-rich ices: Formation of large complex organic molecules in astronomical environments

“…Consequently, the peaks at 1024. 4 respectively, which is in good agreement with our assignments, concerning methanol and ethanol.…”

“…Similar investigations carried out by Lin et al 4 underlined the formation of large carbon chains up to 20 carbon atoms and other various radical saturated and unsaturated hydrocarbons. The cryogenic synthesis of CH, CH 2 , CH 3 , C 2 H 2 , CH 2 H 3 , C 2 H 4 , C 2 H 5 and C 2 H 6 has been examined by Bennett et al 5 through energetic electrons irradiation of pure methane ices to mimic the role of cosmic-ray particles in the chemical transformation of methane which can be the source of large complex molecules including prebiotic species 6 .…”

“…As the present study is devoted to emphasize the influence of water molecules in the photodecomposition of the solid methane, one should pay attention on the main photoproducts realized from the irradiation of methane ice which has been largely investigated previously 4,5,14 . As mentioned in the introduction part, many laboratory simulations of energetic decomposition of pure methane ice have been explored in order to underline the role of CH 4 fragmentation in the formation of complex organic molecules on the surfaces of icy bodies in the interstellar medium, comets and solar system objects.…”

“…As mentioned in the introduction part, many laboratory simulations of energetic decomposition of pure methane ice have been explored in order to underline the role of CH 4 fragmentation in the formation of complex organic molecules on the surfaces of icy bodies in the interstellar medium, comets and solar system objects. In this context, using infrared absorption signatures to indentify the photoproducts, Lin et al 4 16 . In the case of water, the bending mode of H 2 O at 1600 cm -1 has been used with the band strength of 1.2 10 -17 cm molecules -1 taken from Gerakines et al investigations 17 (the same value has been also predicted by DFT calculations for water monomer 18 ).…”

XUV photodesorption of carbon cluster ions and ionic photofragments from a mixed methane–water ice

“…We observe ions with n values of up to 12, as limited by the range of our ToF mass spectrometer. The formation of neutral C n clusters as a result of the VUV (l = 120 nm) photolysis of solid methane has been observed recently by Lin et al 43 They exposed CH 4 dispersed in solid neon at a molar ratio of 1 : 1000 to synchrotron radiation and observed, through infrared spectroscopy, the signatures of carbon clusters and hydrocarbon molecules. In the present case, as discussed above, the starting point for the carbon chemistry is likely the single photon ejection of a proton from the CH 4 molecule.…”