Molecular Hydrogen Formation on Low Temperature Surfaces in Temperature Programmed Desorption Experiments

TL;DR

This paper investigates how molecular hydrogen forms on amorphous silicate surfaces at low temperatures using temperature-programmed desorption experiments, providing insights relevant to astrochemistry and interstellar dust processes.

Contribution

It presents a novel analysis of H_2 formation on amorphous silicate surfaces using TPD and rate equations, determining activation energies with a single isotope model.

Findings

Activation energies for diffusion and desorption of H atoms were obtained.

A single isotope model accurately describes the formation process.

Results can be used to estimate H_2 formation rates in interstellar clouds.

Abstract

The study of the formation of molecular hydrogen on low temperature surfaces is of interest both because it allows to explore elementary steps in the heterogeneous catalysis of a simple molecule and because of the applications in astrochemistry. Here we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations and the activation energies of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results can thus be used to evaluate the formation rate of H_2 on dust grains under the actual conditions present in interstellar clouds.