Methanol formation via oxygen insertion chemistry in ice

Abstract

We present experimental constraints on the insertion of oxygen atoms into methane to form methanol in astrophysical ice analogs. In gas-phase and theoretical studies this process has previously been demonstrated to have a very low or non-existent energy barrier, but the energetics and mechanisms have not yet been characterized in the solid state. We use a deuterium UV lamp filtered by a sapphire window to selectively dissociate O2 within a mixture of O2:CH4 and observe efficient production of CH3OH via O(1D) insertion. CH3OH growth curves are fit with a kinetic model, and we observe no temperature dependence of the reaction rate constant at temperatures below the oxygen desorption temperature of 25K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH4: ~65% of insertions lead to CH3OH with the remainder leading instead to H2CO formation. There is no evidence for CH3 or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH3OH formation from O2 and CH4 diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or non-existent barrier. Oxygen insertion chemistry in ices should therefore be efficient under low-temperature ISM-like conditions, and could provide an important channel to complex organic molecule formation on grain surfaces in cold interstellar regions such as cloud cores and protoplanetary disk midplanes.

References in corpus (9)

• Complex Chemistry in Star-Forming Regions: An Expanded Gas-Grain Warm-up Chemical Model
• Photochemistry and astrochemistry: photochemical pathways to interstellar complex organic molecules
• The cometary composition of a protoplanetary disk as revealed by complex cyanides
• Laboratory evidence for efficient water formation in interstellar ices
• Experimental evidence for Glycolaldehyde and Ethylene Glycol formation by surface hydrogenation of CO molecules under dense molecular cloud conditions
• Vacuum-UV spectroscopy of interstellar ice analogs. I. Absorption cross-sections of polar-ice molecules
• Infrared Spectra and Optical Constants of Astronomical Ices: II. Ethane and Ethylene
• CO diffusion into amorphous H2O ices
• Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules

Cited by in corpus (10)

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• Laboratory and Computational Studies of Interstellar Ices
• Oxygen atom reactions with C2H6, C2H4, and C2H2 in ices
• SO2 and OCS toward high-mass protostars: A comparative study between ice and gas
• A Kinetic Study of the Gas-Phase O( 1 D) + CH3OH and O( 1 D) + CH3CN Reactions. Low Temperature Rate Constants and Atomic Hydrogen Product Yields
• Rethinking Habitability using Biogenic Precursors: Formaldehyde in Millimeter Molecular Clouds of the Inner Galaxy
• Methyl Isocyanate Formation from Oxygen Insertion in Methyl Cyanide Ices
• ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- X. Chemical differentiation among the massive cores in G9.62+0.19