Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 71: Surface Dynamics

O 71.2: Poster

Wednesday, March 18, 2015, 18:15–21:00, Poster A

Thermal desorption studies of ammonia from single crystal and polycrystalline forsterite — •Tushar Suhasaria, John Thrower, and Helmut Zacharias — Physikalisches Institut, WWU Münster, Germany

Olivine [Mg_2xFe_2−2xSiO₄] is an abundant silicate mineral that constitutes a major component of interstellar dust grains [1]. Forsterite [Mg₂SiO₄], the magnesium rich member of the olivine family, is the most abundant of crystalline silicates as suggested by the infrared space observatory (ISO) mission [2]. In cold, dense molecular clouds, various molecules collide with and stick to these dust grains and form icy mantles. Forsterite can thus be used as chemically simple dust grain model to understand the interaction between these adsorbed molecules and the grain surface. In the present work we use temperature programmed desorption (TPD) to investigate the desorption kinetics of ammonia (NH₃) ices on both single crystal and polycrystalline forsterite surfaces. A desorption energy of 25.8 kJmol⁻¹ was obtained for multilayer NH₃ desorption from both surfaces. For the low coverage regime, a distribution of binding energy sites on the forsterite surface was revealed, depending on the nature of the surface. These desorption kinetics parameter are useful to be incorporated into chemical models [3] to understand the gas-grain interaction in more details.

1.Campins, H., & Ryan, E. V. 1989, Astrophys. J., 341, 1059.

2.Molster, F. J., Waters, L. B. F. M., & Tielens, A. G. G. M. 2002, Astron. Astrophys., 382, 222.

3.Garrod, R. T., 2013, Astrophys. J., 765, 60