ESR Spectrum and Structure of the Formyl Radical

TLDR

The formyl radical was generated by photolytic decomposition of HI in CO, by photolysis of formaldehyde in solid argon, and as a product of methyl alcohol photolysis in solid argon. ESR spectra of HCO and DCO in solid CO from 4.2 to 30 K showed temperature‑dependent, broad, unsymmetrical lines with a 137 Oe proton hyperfine splitting, attributed to g‑factor and hyperfine anisotropy, confirming that the formyl radical is not a π‑electron radical.

Abstract

The electron spin resonance (ESR) spectra of the formyl radical (HCO) and the deuterated radical (DCO) have been observed in solid carbon monoxide over the temperature range 4.2° to 30°K. The observed line shapes were temperature dependent, but the cause of the temperature dependence was not definitely determined. The radical was produced by the reaction of CO with hydrogen atoms produced by the photolytic decomposition of HI. The radical was also produced by the photolytic decomposition of formaldehyde in solid argon, and it was found to be one of the products of the photolysis of methyl alcohol in solid argon. The most striking feature of the ESR spectrum of HCO is the very large proton hyperfine splitting (137 oe). Also the lines were broad and unsymmetrical with the linewidth varying from one hyperfine component to the next. It was shown that the line shapes were due to the combination of a rather pronounced anisotropy in the electronic g factor with a smaller anisotropy in the proton hyperfine interaction. These characteristics of the radical gave a good deal of information about its structure which supported the conclusion of other workers that the formyl radical is not a π-electron radical.