Photoprocessing of formamide ice: route towards prebiotic chemistry in
  space
  Aims. Formamide (HCONH2) is the simplest molecule containing the peptide bond
first detected in the gas phase in Orion-KL and SgrB2. In recent years, it has
been observed in high temperature regions such as hot corinos, where thermal
desorption is responsible for the sublimation of frozen mantles into the gas
phase. The interpretation of observations can benefit from information gathered
in the laboratory, where it is possible to simulate the thermal desorption
process and to study formamide under simulated space conditions such as UV
irradiation. Methods. Here, two laboratory analyses are reported: we studied
formamide photo-stability under UV irradiation when it is adsorbed by space
relevant minerals at 63 K and in the vacuum regime. We also investigated
temperature programmed desorption of pure formamide ice in the presence of TiO2
dust before and after UV irradiation. Results. Through these analyses, the
effects of UV degradation and the interaction between formamide and different
minerals are compared.We find that silicates, both hydrates and anhydrates,
offer molecules a higher level of protection from UV degradation than mineral
oxides. The desorption temperature found for pure formamide is 220 K. The
desorption temperature increases to 250 K when the formamide desorbs from the
surface of TiO2 grains. Conclusions. Through the experiments outlined here, it
is possible to follow the desorption of formamide and its fragments, simulate
the desorption process in star forming regions and hot corinos, and constrain
parameters such as the thermal desorption temperature of formamide and its
fragments and the binding energies involved. Our results offer support to
observational data and improve our understanding of the role of the grain
surface in enriching the chemistry in space.
