Fitting multiple datasets in kinetics: n-butane + OH → products

Abstract

Offsets due to systematic calibration errors are a common feature of the literature on temperature-dependent rate constants. We present a formalism for dealing with these offsets within the context of least-squares fitting, using a priori parameter constraints based on the estimated accuracy of individual studies. This methodology not only eliminates biases caused by calibration errors, it also ensures that the metric used to compare different studies is their accuracy, not their precision. Consequently, studies with single measurements at room temperature can be meaningfully compared with studies comprising dozens of measurements spanning a wide temperature range. We apply this procedure to the complete literature dataset for two reactions: OH + propane and OH + n-butane, after first presenting new data for OH + n-butane spanning the temperature range 180–300 K and extending the low-temperature limit of the literature by 50 K. There is outstanding agreement among a very large set of studies, including relative measurements of the propane:n-butane rate constant ratio. We present new reduced transition state theory fits for each reaction that accurately reproduce the observed rate constants between 180 and 1000 K, and argue that these two reactions are the optimal reference reactions for many relative rate studies. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 259–272, 2004