First detection of vibrational spectra of the vinyl and hexatriynyl radicals

Abstract

The first vibrational spectrum of the C$\sb2$H$\sb3$ (vinyl) radical has been identified in an FTIR study of the vacuum ultraviolet (VUV) photolysis products of ethylene (C$\sb2$H$\sb4)$ and its D- and $\sp{13}$C-substituted isotopomers and acetylene (C$\sb2$H$\sb2)$ + HI trapped in Ar at 10 K. Absorptions at 900.2 and 685.4 cm$\sp{-1}$ have been assigned to the $\nu\sb8(a\sp{\prime\prime}),$ out-of-plane wagging and the $\nu\sb7(a\sp\prime),$ in-plane asymmetric CH$\sb2$ bending - $\alpha$CH bending modes. The assignments are supported by the isotopic data and by comparison with the results of a GVB ab initio calculation by Dupuis and Wendoloski, and an MBPT(2) ab initio calculation. A similar FTIR study of the products of the VUV photolysis of acetylene (C$\sb2$H$\sb2)$ and 1,3-butadiene (C$\sb4$H$\sb6)$ trapped in solid Ar has resulted in the first identification of a vibration of the C$\sb6$H (hexatriynyl) radical at 1953.4 cm$\sp{-1}.$ Various D and $\sp{13}$C isotopomers have been observed. The complex, overlapping spectra resulting from partial $\sp{13}$C substitution have been fitted using a force constant adjustment calculation and support the assignment of the 1953.4 cm$\sp{-1}$ absorption to a C$\equiv$C stretching fundamental of linear C$\sb6$H.