ESR of the triplet molecules CCO and CNN in rare-gas matrices; isotope and matrix effects

Publisher Website
Google Scholar
Abstract
CCO and CNN, with isotopic substitution of 13C, 18O, and 15N, were prepared by the reaction of C atoms with CO or N2 and trapped in various matrices at 4 °K. ESR spectra of both 3Σ molecules yielded hyperfine splittings, g values, and zero‐field splittings. In solid neon, these parameters for CαCβO, assuming g∥=ge, were g⊥=2.0029(4), D=0.7392(4) cm−1, ‖A⊥(Cα) ‖ = 57(3) MHz, ‖A∥(Cα) ‖ = 17(3) MHz, ‖A⊥(Cβ) ‖ = 26(3) MHz, ‖A∥(Cβ) ‖ = 32(3) MHz. Similar but less extensive data were obtained for CNαNβ where in solid neon, assuming g∥ =g⊥=ge, D = 1.1590(5) cm−1, ‖A⊥(14Nα) ‖ = 35(5), ‖A⊥(14Nβ) ‖ = 19(5), and ‖A⊥(13C) ‖ = 50(5) MHz. D values for isotopic molecules 12C12C16O, 13C12C18O, etc., varied by small but significant amounts (up to about 0.001 cm−1) in Ne and in Ar matrices. These variations could be approximately accounted for by assuming torsional oscillation in the solid. This was supported by a temperature variation study. The observed decrease of Dgas = 0.772 cm−1 for C2O in matrices, particularly large in Kr and Xe, is attributed partially to motional averaging and partially to matrix perturbations of molecular electronic properties. Theory was applied to qualitatively account for the changes in spin–spin, DSS, and spin–orbit, DSO, contributions to the zfs of the molecule in the solids. Matrix effects are expected to increase DSS and decrease DSO (for positive D) so that the dominant electronic effect is the spin–orbit mixing‐in of singlet states via the matrix.