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Pure ices of amorphous methanol, CH 3 OH(X 1 A 0 ), were irradiated at 11 K by 5 keV electrons at 100 nA for 1 hr. These energetic electrons simulate electronic energy transfer processes that occur as interstellar ices, comets, and icy solar system bodies are subjected to irradiation from MeV ions and secondary electrons produced in this process. The results were analyzed quantitatively via absorption-reflection-absorption Fourier transform infrared ( FTIR) spectroscopy, with the identification of new species aided by high-level electronic structure calculations. The unimolecular decomposition of methanol was found to proceed via the formation of (1) the hydroxymethyl radical, CH 2 OH(X 2 A 00 ), and atomic hydrogen, H( 2 S 1=2 ), (2) the methoxy radical, CH 3 O(X 2 A 0 ), plus atomic hydrogen, (3) formaldehyde, H 2 CO(X 1 A 1 ) plus molecular hydrogen, H 2 (X 1 AE þ g ), and (4) the formation of methane, CH 4 (X 1 A 1 ), together with atomic oxygen, O( 1 D). The accessibility of the last channel indicates that the reverse process, oxygen addition into methane to form methanol, should also be feasible. A kinetic model is presented for the decomposition of methanol into these species, as well as the formyl radical, HCO(X 2 A 0 ), and carbon monoxide, CO(X 1 AE þ ). During the subsequent warming up of the sample, radicals previously generated within the matrix were mobilized and found to recombine to form methyl formate, CH 3 OCHO(X 1 A 0 ), glycolaldehyde, CH 2 OHCHO(X 1 A 0 ), and ethylene glycol, HOCH 2 CH 2 OH(X 1 A). Upper limits for the production of these species by the recombination of neighboring radicals produced during irradiation as well as during the warm-up procedure are presented. The generation of these molecules by irradiation of ices in the solid state and their subsequent sublimation into the gas phase can help explain their high abundances as observed toward hot molecular cores and underlines their importance in astrobiology.

Pure methane ices (CH 4 ) were irradiated at 10 K with energetic electrons to mimic the energy transfer processes that occur in the track of the trajectories of MeV cosmic-ray particles. The experiments were monitored via an FTIR spectrometer (solid state) and a quadrupole mass spectrometer (gas phase). Combined with electronic structure calculations, this paper focuses on the identification of CH x (x ¼ 1Y4) and C 2 H x (x ¼ 2Y6) species and also investigates their formation pathways quantitatively. The primary reaction step is determined to be the cleavage of a carbonhydrogen bond of the methane molecule to form a methyl radical (CH 3 ) plus a hydrogen atom. Hydrogen atoms recombined to form molecular hydrogen, the sole species detected in the gas phase during the irradiation exposure. In the matrix two neighboring methyl radicals can recombine to form an internally excited ethane molecule (C 2 H 6 ), which either can be stabilized by the surrounding matrix or was found to decompose unimolecularly to the ethyl radical (C 2 H 5 ) plus atomic hydrogen and then to the ethylene molecule (C 2 H 4 ) plus molecular hydrogen. The initially synthesized ethane, ethyl, and ethylene molecules can be radiolyzed subsequently by the impinging electrons to yield the vinyl radical (C 2 H 3 ) and acetylene (C 2 H 2 ) as degradation products. Upon warming the ice sample after the irradiation, the new species are released into the gas phase, simulating the sublimation processes interstellar ices undergo during the hot core phase or comets approaching perihelion. Our investigations also aid the understanding of the synthesis of hydrocarbons likely to be formed in the aerosol particles and organic haze layers of hydrocarbon-rich atmospheres of planets and their moons such as Titan.