EPR Study of NO Adsorbed on Magnesium Oxide

Abstract

The EPRspectra of two paramagnetic species were observed when nitric oxide was adsorbed on high‐surface‐area magnesium oxide. The spectrum of one species which is interpreted as NO2 2− was observed at room temperature on MgO that had been degassed at 800°C. It was characterized by gxx =gyy =2.0068, gzz =2.0025, and axx ≃ayy ≃0 G; for 14NO adsorbed azz =43 G while for 15NO adsorbed azz =61 G. The other radical is identified as the adsorbed NO molecule in a strong field at the surface such that the spin—orbit coupling is partially quenched. Its spectrum was observed only at low temperatures (−180°), and was characterized by gxx =gyy =1.995 with gzz =1.90 for MgO degassed at 800° or at 300°C. For 14NO, axx =33 G and azz <10 G while for 15NO, axx =47 G and azz <10 G. Theoretical predictions as well as the spectra of the isoelectronic N2 − molecule—ion are in accord with the assignment of this spectrum. Both paramagnetic species could be partially removed by degassing the sample at room temperature, notwithstanding the rather strong electronic interactions which are indicated by the spectra.