Simultaneous kinetics and ring-down: Rate coefficients from single cavity loss temporal profiles

Cavity ring-down spectroscopy is a recently developed technique for highly sensitive detection of atomic and molecular absorptions. Here, we demonstra te the application of this technique to the measurement of kinetics that oc cur on the same time scale as the loss of light intensity from an optical c avity. We report rate constants for the reactions NO + NO3 --> 2NO(2) and O H + HNO3 --> H2O + NO3 at 296 K, measured as a test of this method. Observe d ring-down profiles with a changing absorber concentration match calculate d profiles, and fits to these profiles produce rate constants that agree wi th literature values to within the uncertainty of the measurements. The tec hnique is general and should provide a simple means of measuring kinetic pa rameters for fast reactions. We also note the possible uses of this method for a variety of kinetics experiments and the outlook for future improvemen ts.