2009MNRAS.394.1510T

Experimental results on the thermal desorption of benzene (C₆H₆) from amorphous silica (SiO₂) are presented. The amorphous SiO₂substrate was imaged using atomic force microscopy, 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 C₆H₆ice. The low-coverage experiments reveal complicated desorption behaviour that results from both porosity and roughness in the SiO₂substrate, and repulsive interactions between C₆H₆molecules. 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. C₆H₆was 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 SiO₂having little impact on the desorption beyond the first few layers.