Radiation-induced transformations of HCN•••C2H2, HCN•••C2H4 and HCN•••C2H6 complexes in noble gas matrices: Synthesis of C3HxN molecules in cryogenic media

The nitrogen containing molecules of general structure C3HxN are important astrochemical species, which occur in interstellar and other extraterrestrial media. In this work, we have first demonstrated the formation of a number of nitrites and isonitriles (C2H3CN, C2H3NC and C2H5NC) through a direct radiation-induced synthesis from the matrix isolated intermolecular complexes HCN center dot center dot center dot C2Hn = 2, 4, 6) at 6 K. The deposited matrices Ng/HCN/C2Hn (Ng = Ar, Kr or Xe) were irradiated with X-rays and the formation of products was monitored by FTIR spectroscopy. In addition to synthetic products (C3HxN molecules), irradiation results in dehydrogenation of the initial complexes and their isomerization to the corresponding HNC center dot center dot center dot C2Hn complexes. The formation of propionitrile (C2H5CN) also cannot be excluded, although this molecule was not detected experimentally, possibly due to its poor IR absorption coefficients. Cyanoacetylene (HC3N) is accumulated with an induction period and becomes predominating at high absorbed doses, which points to its formation from the radiation-induced decomposition of the primary products. The obtained results suggest new possible routes for formation of nitrites, isonitriles and cyanoacetylene in complex astrochemical ices.

Automated summary

This study demonstrates the formation of nitrites and isonitriles from matrix isolated intermolecular complexes through direct radiation-induced synthesis at 6 K. In addition to synthetic products, irradiation also results in dehydrogenation and isomerization of the initial complexes, leading to the formation of propionitrile and cyanoacetylene. These results suggest new possible routes for the formation of these molecules in complex astrochemical ices.