ESR study of CO adsorption on thoria

Electron spin resonance (ESR) study of 12CO and 13CO adsorbed on thoria between 25 and 300 °C shows that part of the adsorbate exists in the form of a paramagnetic axial radical, the unpaired electron of which is located in a π orbital. Two types of adsorbed CO are detected by ESR, for which the unpaired electron is, respectively, 33 and 15% on the carbon atom. These observations are consistent with the previous hypothesis of a positively charged CO adsorbate on thoria.