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 (rateOD/rateOH = 1.6) on SiO2 didnotscale as predicted by the theoretical models (rateOD/rateOH = 13). Recent measurements of isotopically substituted silanols (R3SiOH and R3SiOD dilute in CCl4) 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 wavelengths with improved temporal resolution are discussed.
© 1986 Optical Society of America
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