Abstract

Time-resolved measurements of vibrational relaxation rates have determined the population decay of vibrationally excited OH groups: adsorbed on high surface area SiO₂; in model silanols; and as defect sites in quartz.¹ Depopulation of the vibrationally excited OH oscillator was found to occur on a time scale of 80-300 ps. The temperature dependence of the vibrational relaxation rates in quartz (OH) and on SiO₂ (OH and OD) were all found to follow a simple multiphonon relaxation model.² However, the relative rates for the two isotopes (rate_OD/rate_OH = 1.6) on SiO₂ did not scale as predicted by the theoretical models (rate_OD/rate_OH = 13). Recent measurements of isotopicaliy substituted silanols (R₃SiOH and R₃SiOD dilute in CCI₄) also find OD decay times comparable with those of OH. The observed decay rates appear to be dominated by processes which proceed through a SiOH bending mode. Prospects for extending these methods to longer wavelength with improved temporal resolution are discussed.

© 1986 Optical Society of America