Issue 31, 2010

A kinetic study of reactions of calcium-containing molecules with O and H atoms: implications for calcium chemistry in the upper atmosphere

Abstract

This paper describes the kinetic study of a number of gas-phase reactions involving neutral Ca-containing species, many of which are important for describing the chemistry of meteor-ablated calcium in the Earth's upper atmosphere. Ca atoms were produced thermally in the upstream section of a fast flow tube, and then converted to the molecular species CaO, CaO2, CaO3, CaCO3 or Ca(OH)2 by the addition of appropriate reagents. Atomic O or H was added further downstream, and both Ca and CaO were detected at the downstream end of the flow tube by laser-induced fluorescence. The following rate coefficients were determined: k(CaO + O → Ca + O2) = (3.1+2.0−1.5) × 10−10 at 300 K and (1.3+3.4−0.6) × 10−10 at 203 K; k(CaO2 + OCaO + O2) = (2.2+7.0−1.4) × 10−11 at 300 K and (1.6+2.9−0.7) × 10−11 at 203 K; k(CaO2 + H → products, 298 K) = (1.2 ± 0.6) × 10−11; k(CaCO3 + O → CaO2 + CO2, 300 K) ≤ 1.0 × 10−12; k(CaCO3 + H→ CaOH + CO2, 298 K) ≥ 2.8 × 10−12 and ≤3.6 × 10−11; k(CaO3 + H→ CaOH + O2, 298 K) ≥ 1.7 × 10−11; k(Ca(OH)2 + HCaOH + H2O, 298 K) ≥ 1.1 × 10−11; k(CaOH + H → Ca + H2O, 298 K) ≥ 1.1× 10−11 cm3 molecule−1 s−1. The kinetics of the reactions of Ca and CaO with NO2 and N2O were also studied, yielding k(Ca + NO2CaO + NO) = (2.6 ± 0.3) × 10−10 at 300 K and (2.0 ± 0.3) × 10−10 at 203 K; k(CaO + NO2 → CaO2 + NO) = (8.1 ± 2.0) × 10−10 at 300 K and (2.9 ± 1.0) × 10−10 at 202 K; k(CaO + N2O → CaO2 + N2) = (4.2 ± 1.7) × 10−11 at 300 K and (2.2 ± 1.2) × 10−12 at 206 K; k(CaO + H2 → Ca + H2O, 300 K) = (3.4 ± 1.3) × 10−10 cm3 molecule−1 s−1. Electronic structure calculations of the relevant potential energy surfaces were performed to interpret the experimental results, and the atmospheric implications of these measurements are then discussed.

Graphical abstract: A kinetic study of reactions of calcium-containing molecules with O and H atoms: implications for calcium chemistry in the upper atmosphere

Supplementary files

Article information

Article type
Paper
Submitted
18 Mar 2010
Accepted
14 May 2010
First published
08 Jun 2010

Phys. Chem. Chem. Phys., 2010,12, 9094-9106

A kinetic study of reactions of calcium-containing molecules with O and H atoms: implications for calcium chemistry in the upper atmosphere

S. L. Broadley and J. M. C. Plane, Phys. Chem. Chem. Phys., 2010, 12, 9094 DOI: 10.1039/C004451B

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