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

Abstract

The CH _3 O and CH _2 OH 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 CH _3 O to CH _2 OH is crucial for a better understanding of the chemical evolution into various COMs. Recent work suggested that the reaction between CH _3 OH and OH on ice dust plays an important role in forming CH _3 O and CH _2 OH radicals. However, quantitative details on the abundance of these radicals have not been presented to date. Herein, we experimentally determined the branching ratio (CH _3 O/CH _2 OH) resulting from the CH _3 OH + OH reaction on the water ice surface at 10 K to be 4.3 ± 0.6. Furthermore, the CH _3 O 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.

Keywords

• Dense interstellar clouds
• Interstellar dust processes
• Astrochemistry