Unstable intermediates. Part LXXIX. Electron spin resonance studies of the effect of environment upon the hyperfine parameters for CO2 ? and NO2

Exposure of alkali and alkaline-earth metal formates to 60Co γ-radiation gave e.s.r. spectra characteristic of CO2– radicals. These results are compared with those previously published for CO2– in various matrices and with a range of results for NO2 in different environments. Both radicals rotate or librate extensively, but after these movements have been quenched or allowed for, the effect of the environment upon the spin-density distributions and 2p/2s could be gauged. The results for CO2– were markedly dependent upon the nature of the host lattice, but those for the isoelectronic NO2 radical were almost independent of environment. This difference is presumed to be a result of the negative charge of the former radical and of the consequent large crystal fields that it experiences.The e.s.r. spectra of γ-irradiated alkali-metal formates exhibit well resolved hyperfine coupling to the cation nuclei. Trends in the spin-densities derived therefrom are discussed.