Infrared spectra of UV photolysed cyanoacetylene and dicyanoacetylene trapped in argon matrices at 10 K have been performed. From cyanoacetylene photolysed at lambda > 120 nm, we obtained three different isomers. The formation of HCCNC, HNCCC and the exotic one CCNCH is observed. In the case of photodissociation of dicyanoacetylene at lambda > 235 nm, three others isomers were isolated: NCCCNC, CNCCNC and the higher energy one CCCNCN. The identification of isomers is based on B3LYP/6-31g** density functional study and deuterium experiment for cyanoacetylene. (C) 2002 Elsevier Science B.V. All rights reserved.