Electron Spin Resonance Study of Surface Defects of Silica Gel Formed by Gas Discharges

Surface defects of silica gel formed by a microwave electric discharge in a stream of oxygen and of nitrogen have been studied by means of electron spin resonance (e.s.r.) spectroscopy. The magnetic center is identified as a hole trapped by a surface oxygen atom which is formed by the removal of a hydrogen atom from a hydroxyl group. The principal values of the g-tensor were found to be gxx = 2.037, gyy = 2.008, and gzz = 2.002, respectively, where the direction of x-axis was taken along the O—Si bond. The center has a weak hyperfine interaction with a hydrogen nucleus of an adjacent hydroxyl group. The hyperfine splitting is 15 Oe.