Reaction Kinetics of CaOH with H and O(2) and O(2)CaOH with O: Implications for the Atmospheric Chemistry of Meteoric Calcium

[Image: see text] The ablation of cosmic dust particles entering the Earth’s upper atmosphere produces a layer of Ca atoms around 90 km. Here, we present a set of kinetic experiments designed to understand the nature of the Ca molecular reservoirs on the underside of the layer. CaOH was produced by laser ablation of a Ca target in the fast flow tube and detected by non-resonant laser-induced fluorescence, probing the D((2)Σ(+)) ← X((2)Σ(1)) transition at 346.9 nm. The following rate constants were measured (at 298 K): k(CaOH + H → Ca + H(2)O) = (1.04 ± 0.24) × 10(–10) cm(3) molecule(–1) s(–1), k(CaOH + O → CaO + OH) < 1 × 10(–11) cm(3) molecule(–1) s(–1), and k(CaOH + O(2) → O(2)CaOH, 1 Torr) = (5.9 ± 1.8) × 10(–11) cm(3) molecule(–1) s(–1) (uncertainty at the 2σ level of confidence). The recycling of CaOH from reaction between O(2)CaOH and O proceeds with an effective rate constant of k(eff)(O(2)CaOH + O → CaOH + products, 298 K) = 2.8(–1.2)(+2.0) × 10(–10) cm(3) molecule(–1) s(–1). Master equation modeling of the CaOH + O(2) kinetics is used to extrapolate to mesospheric temperatures and pressures. The results suggest that the formation of O(2)CaOH slows the conversion of CaOH to atomic Ca via reaction with atomic H, and O(2)CaOH is likely to be a long-lived reservoir species on the underside of the Ca layer and a building block of meteoric smoke particles.