A. Jiménez-Escobar, G. M. Muñoz Caro
This work aims to study the unexplained sulfur depletion observed toward
dense clouds and protostars. We made simulation experiments of the
UV-photoprocessing and sublimation of H2S and H2S:H2O ice in dense clouds and
circumstellar regions, using the Interstellar Astrochemistry Chamber (ISAC), a
state-of-the-art ultra-high-vacuum setup. The ice was monitored in situ by
mid-infrared spectroscopy in transmittance. Temperature-programmed desorption
(TPD) of the ice was performed using a quadrupole mass spectrometer (QMS) to
detect the volatiles desorbing from the ice. Comparing our laboratory data to
infrared observations of protostars we obtained a more accurate upper limit of
the abundance of H2S ice toward these objects. We determined the desorption
temperature of H2S ice, which depends on the initial H2S:H2O ratio.
UV-photoprocessing of H2S:H2O ice led to the formation of several species.
Among them, H2S2 was found to photodissociate forming S2 and, by elongation,
other species up to S8, which are refractory at room temperature. A large
fraction of the missing sulfur in dense clouds and circumstellar regions could
thus be polymeric sulfur residing in dust grains.
View original:
http://arxiv.org/abs/1112.3240
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