Spectroscopic characterization of the complex of vinyl radical and carbon dioxide : Matrix isolation and ab initio study

We report on the preparation and vibrational characterization of the C2H3 center dot center dot center dot CO2 complex, the first example of a stable intermolecular complex involving vinyl radicals. This complex was prepared in Ar and Kr matrices using UV photolysis of propiolic acid (HC3OOH) and subsequent thermal mobilization of H atoms. This preparation procedure provides vinyl radicals formed exclusively as a complex with CO2, without the presence of either CO2 or C2H3 monomers. The absorption bands corresponding to the nu(5)(C2H3), nu(7)(C2H3), nu(8)(C2H3), nu(2)(CO2), and nu(3)(CO2) modes of the C2H3 center dot center dot center dot CO2 complex were detected experimentally. The calculations at the UCCSD(T)/L2a level of theory predict two structures of the C2H3 center dot center dot center dot CO2 complex with C-s and C-1 symmetries and interaction energies of -1.92 and -5.19 kJ mol(-1). The harmonic vibrational frequencies of these structures were calculated at the same level of theory. The structural assignment of the experimental species is not straightforward because of rather small complexation-induced shifts and matrix-site splitting of the bands (for both complex and monomers). We conclude that the C-1 structure is the most probable candidate for the experimental C2H3 center dot center dot center dot O-2 complex based on the significant splitting of the bending vibration of CO2 and on the energetic and structural considerations. Published by AIP Publishing.Peer reviewe