Formation of molecular hydrogen on amorphous silicate surfaces

TL;DR

This study investigates how amorphous silicate surfaces facilitate molecular hydrogen formation, revealing higher energy barriers and efficiency differences compared to polycrystalline silicates, with implications for interstellar chemistry.

Contribution

It provides experimental data and a rate equation model for hydrogen formation on amorphous silicates, highlighting the impact of grain morphology on catalytic efficiency.

Findings

Higher energy barriers for diffusion and desorption on amorphous silicates.

Amorphous silicate grains are efficient catalysts of H₂ formation in diffuse clouds.

Differences in grain morphology significantly affect hydrogen formation efficiency.

Abstract

Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained for polycrystalline silicates, demonstrating the importance of grain morphology. Using these barriers we evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorphous silicate grains are efficient catalysts of H_2 formation in diffuse interstellar clouds.