  Context. The chemical evolution of formamide (HCONH2), a molecule of
astrobiological interest that has been tentatively identified in interstellar
ices and in cometary coma, has been studied in laboratory under simulated
astrophysical conditions such as ion irradiation at low temperature.
  Aims. To evaluate the abundances of formamide observed in space or in
laboratory, the integrated absorbances for all the principal IR features of
frozen amorphous pure formamide deposited at 20 K were measured. Further
evidence that energetic processing of ices occurring in space is extremely
relevant both to astrochemistry and to astrobiology has been found, showing
that new molecular species are synthesized by ion irradiation at a low
temperature.
  Methods. Pure formamide were deposited at 20 K and IR transmission spectra
measured for different ice thicknesses. The ice thickness was derived by
looking at the interference pattern (intensity versus time) of a He-Ne laser
beam reflected at an angle of 45 deg by the vacuum-film and film-substrate
interfaces. Samples of formamide ice were irradiated with 200 keV H+ ions and
IR spectra recorded at different ion fluences.
  Results. New molecules were synthesized among which are CO, CO2, N2O,
isocyanic acid (HNCO), and ammonium cyanate (NH4+OCN-). Some of these species
remain stable after warming up to room temperature.
