# A study of methanol and silicon monoxide production through episodic explosions of grain mantles in the Central Molecular Zone

## TL;DR

This study explores episodic grain mantle explosions as a mechanism for methanol and silicon monoxide production in the Central Molecular Zone, aligning models with observed abundances and suggesting a cyclic desorption process.

## Contribution

It introduces a novel episodic explosion model for grain mantles that explains methanol and SiO abundances without additional mechanisms.

## Key findings

- Episodic explosions reproduce observed methanol levels.
- Methanol forms mainly via hydrogenation of CO on grains.
- High silicon depletion explains SiO observations.

## Abstract

Methanol (CH$_3$OH) is found to be abundant and widespread towards the Central Molecular Zone, the inner few hundred parsecs of our Galaxy. Its origin is, however, not fully understood. It was proposed that the high cosmic ray ionisation rate in this region could lead to a more efficient non-thermal desorption of this species formed on grain surfaces, but it would also mean that this species is destroyed in a relatively short timescale. In a first step, we run chemical models with a high cosmic ray ionisation rate and find that this scenario can only reproduce the lowest abundances of methanol derived in this region ($\sim$10$^{-9}$-10$^{-8}$). In a second step, we investigate another scenario based on episodic explosions of grain mantles. We find a good agreement between the predicted abundances of methanol and the observations. We find that the dominant route for the formation of methanol is through hydrogenation of CO on the grains followed by the desorption due to the grain mantle explosion. The cyclic aspect of this model can explain the widespread presence of methanol without requiring any additional mechanism. We also model silicon monoxide (SiO), another species detected in several molecular clouds of the Galactic Centre. An agreement is found with observations for a high depletion of Si (Si/H $\sim$ 10$^{-8}$) with respect to the solar abundance.