TIME-RESOLVED RESONANCE RAMAN-SPECTROSCOPY OF THE CARBONATE RADICAL

The literature contains conflicting evidence regarding the protonation state of the carbonate radical, a species which now appears to be of biological significance. The time-resolved resonance Raman spectrum of CO3.- has been observed. The radical was produced by oxidation of bic arbonate and carbonate using sulfate radicals at pH values from 7.5 to 12.3. The resonance Raman spectrum was found to be invariant with pH and contains a strongly polarised and intense band at 1062 cm(-1). The spectrum is consistent with the radical having C-2v symmetry, indicat ing some distortion from the predicted D-3h structure. The data sugges t that the carbonate radical (CO3.-) formed by one-electron oxidation of bicarbonate and carbonate does not undergo protonation to the conju gate acid, HCO3., as previously suggested with a pk(a) of 9.6. Some bi ochemical consequences of this are discussed.