UV-induced growth of cyanopolyyne chains in cryogenic solids

Abstract

UV laser excitation of cryogenic solids doped with cyanoethyne, HC₃N, led to an in situ creation of longer carbon–nitrogen chains, namely HC₅N, C₄N₂, and C₆N₂, heralded by their strong visible luminescence. HC₅N and C₄N₂ molecules can form, most probably, within HC₃N aggregates linked by hydrogen bonds, while the reaction occurring between two isolated, photochemically created C₃N radicals yields C₆N₂. This latter species, dicyanobutadiyne, is easily detected in Ar, Kr, N₂, as well as in parahydrogen solids. The C₆N₂ phosphorescence is identified here for the first time. The reported carbon chain coupling reactions in rigid environments are of interest for astrochemistry of interstellar ices.