Determination of the Branching Ratio of CH₃OH + OH Reaction on Water Ice Surface at 10 K

Abstract

The CH3O and CH2OH radicals can be important precursors of complex organic molecules (COMs) in interstellar dust. The COMs presumably originating from these radicals were abundantly found in various astronomical objects. Because each radical leads to different types of COMs, determining the abundance ratio of CH3O to CH2OH is crucial for a better understanding of the chemical evolution into various COMs. Recent work suggested that the reaction between CH3OH and OH on ice dust plays an important role in forming CH3O and CH2OH radicals. However, quantitative details on the abundance of these radicals have not been presented to date. Herein, we experimentally determined the branching ratio (CH3O/CH2OH) resulting from the CH3OH + OH reaction on the water ice surface at 10 K to be 4.3 ± 0.6. Furthermore, the CH3O product in the reaction would participate in subsequent diffusive reactions even at a temperature as low as 10 K. This fact should provide critical information for COMs formation models in cold molecular clouds.