A KINETIC INVESTIGATION OF THE REACTION CA + O-3 OVER THE TEMPERATURE-RANGE 213-K-383-K

The reaction Ca + O3 --> CaO + O2 has been studied by the pulsed multiphoton dissociation of calcium acetylacetonate vapour at 193.3 nm, which produced Ca atoms in an excess of O3 and He bath gas. The reaction was then followed either by time-resolved laser-induced fluorescence spectroscopy of atomic Ca at 422.7 nm [Ca(4P-1(1)-4(1)S)], or by time-resolved molecular chemiluminescence at lambda > 695 nm [CaO(A 1SIGMA+-X 1SIGMA+), DELTAv < 4]. The rate coefficient is given by k(212 < T/K < 384) = (8.23 +/- 1.08) x 10(-10) exp[-(1600 +/- 300) J mol-1/RT] cm3 molecule-1 s-1, where the quoted uncertainties are 2sigma. This result is then compared to the predictions of long-range capture theory. Finally, there is a discussion of the impact of this reaction on the chemistry of meteor-ablated calcium in the upper atmosphere.