2017/06/29 by Jennifer B. Bergner, Karin I. Öberg, Karin I. Oberg +1 · 2 citations
Earth and Planetary Sciences · Physics and Astronomy · #Astro and Planetary Science #Astrochemistry #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Desorption #Dissociation (chemistry) #Hydrocarbon #Kinetic energy #Methane #Methanol #Molecule #Oxygen #Reaction rate constant #astro-ph.EP #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aa7d09
arxiv created 2017/06/29 · openalex created_date 2017/07/14 · openalex publication_date 2017/08/09 · arxiv updated 2017/08/23 · openalex updated_date 2026/08/05
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 nonexistent 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 O 2 within a mixture of O 2 :CH 4 and observe efficient production of CH 3 OH via O( 1 D) insertion. CH 3 OH 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 25 K. Through an analysis of side products we determine the branching ratio of ice-phase oxygen insertion into CH 4 : ∼65% of insertions lead to CH 3 OH, with the remainder leading instead to H 2 CO formation. There is no evidence for CH 3 or OH radical formation, indicating that the fragmentation is not an important channel and that insertions typically lead to increased chemical complexity. CH 3 OH formation from O 2 and CH 4 diluted in a CO-dominated ice similarly shows no temperature dependence, consistent with expectations that insertion proceeds with a small or nonexistent 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.