Single Substitution Kinetic Isotope Effect Measurements For Ch₄ + O(¹d) Using Cavity Ring-down Spectroscopy

As the most abundant atmospheric hydrocarbon and potent greenhouse gas, methane plays a major role in the chemistry of Earth’s atmosphere. The study of kinetic isotope effects (KIEs) for H–D and $^{12}$C–$^{13}$C substitutions on the reaction rates for methane is of importance for modelers, but is challenging because the effects are small, and producing methane oxidants results in a variety of secondary chemistry. In this work, single and double substitution methane KIEs for $^{13}$CH$_{4}$ and CH$_{2}$D$_{2}$ and were produced using the flash photolysis of N$_{2}$O and the methane isotopic compositions were determined via frequency-stabilized cavity ring-down spectroscopy using a dual wavelength near-IR DBF laser system. The KIE of $^{13}$CH$_{4}$ was found to differ with the literature value at room temperature of 1.013 by a factor of two, and the H-D KIE of CH$_{2}$D$_{2}$ was measured for the first time to be 1.098(23). Further, the expected lack of a temperature-dependence of the KIE over the range 170 – 300 K was seen as expected