Kinetic Study of Ni and NiO Reactions Pertinent to the Earth's Upper Atmosphere.

Abstract

Nickel atoms are injected into the Earth's mesosphere by meteoric ablation, producing a Ni layer between 70 and 105 km in altitude. The subsequent reactions of Ni and NiO with atmospherically relevant species were studied using the time-resolved pulsed laser photolysis-laser-induced fluorescence technique, combined with electronic structure calculations and RRKM theory where appropriate. Results for bimolecular reactions (in cm3 molecule-1 s-1): k(Ni + O3, 293 K) = (6.5 ± 0.7) × 10-10; k(NiO + O3 → Ni + 2O2, 293 K) = (1.4 ± 0.5) × 10-10; k(NiO + O3 → NiO2 + O2, 293 K) = (2.5 ± 0.7) × 10-10; k(NiO + CO, 190-377 K) = (3.2 ± 0.6) × 10-11 ( T/200)-0.19±0.05. For termolecular reactions (in cm6 molecule-2 s-1, uncertainty ± σ over the stated temperature range): log10( krec,0(Ni + O2 + N2, 190-455 K)) = -37.592 + 7.168log10( T) - 1.5650(log10( T))2, σ = 11%; log10( krec,0(NiO + O2 + N2, 293-380 K)) = -41.0913 + 10.1064log10( T) - 2.2610(log10( T))2, σ = 22%; and log10( krec,0(NiO + CO2 + N2, 191-375 K)) = -41.4265 + 10.9640log10( T) - 2.5287(log10( T))2, σ = 15%. The faster recombination reaction NiO + H2O + N2, which is clearly in the falloff region over the experimental pressure range (3-10 Torr), is best described by log10( krec,0/cm6 molecule-2 s-1) = -29.7651 + 5.2064log10( T) - 1.7118(log10( T))2, krec,∞ = 6.0 × 10-10 exp(-171/ T) cm3 molecule-1 s-1, broadening factor Fc = 0.84, σ = 16%. The implications of these results in the atmosphere are then discussed.