Infrared study of matrix-isolated ethyl cyanide: simulation of the photochemistry in the atmosphere of Titan

Abstract

Low-temperature Ar matrix isolation has been carried out to investigate the infrared spectrum of ethyl cyanide (CH₃CH₂CN), a molecule present in the atmosphere of Titan. The λ > 120 nm and λ > 230 nm photolysis reactions of ethyl cyanide in an Ar matrix were also performed in order to compare the behaviour of this compound when it is submitted to high and low energetic radiations. These different wavelengths have been used with the aim to reproduce the radiation reaching the various parts of the atmosphere. Several photoproducts have been identified during photolysis such as vinyl cyanide (CH₂CHCN), cyanoacetylene (HC₃N), and ethylene/hydrogen cyanide (C₂H₄/HCN), ethylene/hydrogen isocyanide (C₂H₄/HNC), acetylene/hydrogen cyanide (C₂H₂/HCN), acetylene/hydrogen isocyanide (C₂H₂/HNC), and acetylene:methylenimine (C₂H₂:HNCH₂) complexes. Ethyl isocyanide (CH₃CH₂NC) and a ketenimine form (CH₃CHCNH) have been identified as well. Photoproduct identification and spectral assignments were done using previous studies and density functional theory (DFT) calculations with the B3LYP/cc-pVTZ basis set.