ESR and a b i n i t i o theoretical studies of the cation radicals 12C2 16O+2, 12,13C2 16O+2, 13C2 16O+2, 12C2 16,17O+2, 12C2 17O+2, and 12,13C2 16,17O+2 isolated in neon matrices at 4 K. The use of matrix isolation for trapping ion–neutral reaction products

An experimental procedure for generating and trapping the products of ion–neutral reactions has been developed. The method has been applied to a neon matrix ESR study of the C2O+2 radical (X 2Bu) formed during deposition at 4 K by the reaction CO++CO. Six different isotopic combinations of C2O+2 were studied which allowed a complete characterization of the 13C and 17O nuclear hyperfine structure. The experimental A tensors were compared with the results of an extensive SCF and CI theoretical calculation. A full discussion of the theoretical procedure utilized is presented. The electronic ground state was determined by a CI calculation to be the planar trans configuration with a CCO bond angle of 141°. A description of the MO containing the unpaired electron is presented and compared with CO+ and the isoelectronic anion radical C2N−2. The effects of noncoincidence between the g and A tensors are considered in detail for this powder sample of C2O+2 which exhibited relatively narrow ESR lines in a neon matrix at 4 K. The observed g values were gx=2.0034(2), gy=2.0019(2), and gz=1.9912(2). The effective 13C A parameters observed in the principal g tensor axis system were Ax=577(1), Ay=606(1), and Az=583(1) MHz. Experimental estimates of Ayz varied from about 7 to 32 MHz. The 17O A tensor had components of Ax≊0, ‖Ay‖=74(1) MHz and Az≊0. Analysis of the g tensor for C2O+2 indicates the presence of a low lying excited electronic state (2Au) which is predicted at ≊18 000 cm−1 by an SCF theoretical calculation.