ESR of 17O-Labeled CO2− Radical Trapped in a Single Crystal of Sodium Formate

Abstract

The ESR spectrum of x-irradiated sodium formate enriched in 17O is interpreted in terms of the CO2− radical. Two magnetically inequivalent oxygens were observed. The hyperfine tensors of 13C and 17O were determined and the following principal values were obtained for 13C: 155, 150, and 195 G, respectively, along the axis perpendicular to the molecular plane, along the O–O direction, and along the C2 axis. These results agree with those previously reported. For 17O the magnitudes of the principal values for both oxygens are practically identical, the averages being 22.0, 23.2, and 51.0 G. The direction of the largest value is in the molecular plane inclined at 13° to the C2 axis. The results are used to derive the coefficients of the 4a1 molecular orbital containing the unpaired electron.