Laboratory investigations of the interaction between benzene and bare silicate grain surfaces

TL;DR

This study investigates how benzene interacts with amorphous silica surfaces through temperature programmed desorption experiments, revealing complex desorption behaviors influenced by surface porosity, roughness, and intermolecular interactions, with implications for interplanetary dust particles.

Contribution

It provides detailed kinetic parameters for benzene desorption from silica surfaces, including effects of surface porosity and water coverage, advancing understanding of molecule-surface interactions in space environments.

Findings

Benzene exhibits complex desorption behavior due to surface porosity and roughness.

Water pre-exposure influences benzene adsorption and desorption.

Kinetic parameters align with previous studies, showing minimal impact of silica beyond initial layers.

Abstract

Experimental results on the thermal desorption of benzene (C6H6) from amorphous silica (SiO2) are presented. The amorphous SiO2 substrate was imaged using atomic force microscopy (AFM), revealing a surface morphology reminiscent of that of interplanetary dust particles (IDPs). Temperature programmed desorption (TPD) experiments were conducted for a wide range of C6H6 exposures, yielding information on both C6H6-SiO2 interactions and the C6H6-C6H6 interactions present in the bulk C6H6 ice. The low coverage experiments reveal complicated desorption behaviour that results both from porosity and roughness in the SiO2 substrate, and repulsive interactions between C6H6 molecules. Kinetic parameters were obtained through a combination of direct analysis of the TPD traces and kinetic modelling, demonstrating the coverage dependence of both desorption energy and pre-exponential factor. Experiments were also performed whereby the pores were blocked by pre-exposure of the SiO2 to water vapour. C6H6 was observed to be adsorbed preferentially on the SiO2 film not covered by H2O at the temperature at which these experiments were performed. This observation means that intermolecular repulsion likely becomes important at smaller C6H6 exposures on grains with a H2O mantle. Kinetic modelling of C6H6 multilayer desorption yields kinetic parameters in good agreement with previous studies, with the SiO2 having little impact on the desorption beyond the first few layers.