Determination of the branching ratio of CH$_3$OH + OH reaction on water ice surface at 10 K

TL;DR

This study experimentally determines the branching ratio of radicals formed from CH$_3$OH + OH on water ice at 10 K, providing key data for understanding complex organic molecules in cold space environments.

Contribution

The paper presents the first quantitative measurement of the CH$_3$O/CH$_2$OH radical ratio from this reaction on ice at 10 K, advancing astrochemical models.

Findings

Branching ratio of 4.3 ± 0.6 for CH$_3$O/CH$_2$OH radicals.

CH$_3$O radicals can participate in further reactions at 10 K.

Results inform models of complex organic molecule formation in cold interstellar environments.

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 to 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 $\pm$ 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.