The infrared spectra of C₂H₄⁺ and C₂H₃ trapped in solid neon

When a mixture of ethylene in a large excess of neon is codeposited at 4.3 K with a beam of neon atoms that have been excited in a microwave discharge, two groups of product absorptions appear in the infrared spectrum of the deposit. Similar studies using C₂H₄-1-¹³C and C₂D₄ aid in product identification. The first group of absorptions arises from a cation product which possesses two identical carbon atoms, giving the first infrared identification of two fundamentals of C₂H₄⁺ and three of C₂D₄⁺, as well as a tentative identification of ν₉ of C₂H₄⁺. The positions of these absorptions are consistent with the results of density functional calculations and of earlier photoelectron studies. All of the members of the second group of product absorptions possess two inequivalent carbon atoms. They are assigned to the vinyl radical, C₂H₃, and to C₂D₃, in agreement with other recent infrared assignments for those species.