Thermal processing of formamide ices on silicate grain analogue

Fourier transform-infrared spectroscopy (FT-IR) and temperature programmed desorption (TPD) have been used to examine the thermal processing of three isotopes of pure formamide ice (HCONH2, DCONH2, and HCOND2) adsorbed on a SiO2 interstellar grain analogue. Pure formamide ice on SiO2 nanoparticles displays at least three different phases that we interpret as a porous phase from ∼70-145 K, a compacted polycrystalline phase from ∼145-210 K, and a third slow diffusion and sublimation phase from ∼210-380 K. Possible dimerization is also discussed. Formamide desorption from the SiO2 grain surface is characterized by TPD of pure HCONH2 and mixed H2O:HCONH2 ices. Water desorbs at 160 K, and formamide has a TPD peak maximum at ∼228 K. A mean Eact of ∼14.7 kcal/mol (0.64 eV) was obtained using Redhead analysis, indicating strong intermolecular forces within formamide ice. The mixed H2O:HCONH2 ice TPD data suggests possible formamide accumulation if the grains are exposed to temperature cycles <180 K.