Observation of site-dependent relaxation of the OH vibrational stretch mode in fused silica

We have investigated the vibrational relaxation of the OH impurity stretch mode in amorphous SiO2. At low temperatures, a short relaxation time of ≈10−10 s is found that varies strongly across the inhomogeneously broadened absorption line. The inhomogeneous broadenining is caused by a site-dependent frequency shift proportional to the strength of the hydrogen bond of the OH to neighboring atoms. Thus the observed lifetime decrease across the absorption line can be attributed to increasing hydrogen bond strength. A simple relation between the site-dependent vibrational lifetime and the frequency shift is presented.