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

Abstract

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 nitriles and isonitriles (C2H3CN, C2H3NC and C2H5NC) through a direct radiation-induced synthesis from the matrix isolated intermolecular complexes HCN⋯C2Hn (n = 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⋯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 nitriles, isonitriles and cyanoacetylene in complex astrochemical ices.