Matrix isolation study of the interaction of excited argon atoms with methyl cyanide,vibrational and electronic spectra of ketenimine

When methyl cyanide mixed with an excess of argon is codeposited at 14 K with a beam of argon atoms that has been excited by a low power microwave discharge, infrared and ultraviolet absorptions of several previously unidentified products appear. The most prominent set of absorptions is assigned to ketenimine, previously tentatively identified as the product of the reaction of NH with C₂H₂ in an argon matrix. Using a molecular geometry resulting from a recent ab initio calculation and a valence force field with four interaction constants, it has been possible to obtain a satisfactory least-squares force constant fit to the infrared data for seven isotopic species of ketenimine. Two electronic band systems are also reported for ketenimine, which is photodissociated by 2537-A radiation. The mechanism by which ketenimine is formed may involve an initial electron transfer from excited argon to methyl cyanide. Spectrospic data are also considered for the other products, one of them tentatively identified as CH₂CH, which differ in their behavior on mercury-are photolysis of the sample.