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( k_rec,0(Ni + O₂ + N₂, 190-455 K)) = -37.592 + 7.168log₁₀( T) - 1.5650(log₁₀( T))², σ = 11%; log₁₀( k_rec,0(NiO + O₂ + N₂, 293-380 K)) = -41.0913 + 10.1064log₁₀( T) - 2.2610(log₁₀( T))², σ = 22%; and log₁₀( k_rec,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( k_rec,0/cm⁶ molecule^-2 s^-1) = -29.7651 + 5.2064log₁₀( T) - 1.7118(log₁₀( T))², k_rec,∞ = 6.0 × 10^-10 exp(-171/ T) cm³ molecule^-1 s^-1, broadening factor F_c = 0.84, σ = 16%. The implications of these results in the atmosphere are then discussed.