A study of the reactions of Ni+ and NiO+ ions relevant to planetary upper atmospheres

The reactions between Ni+(2D) and O3, O2, N2, CO2 and H2O were studied at 294 K using the pulsed laser ablation at 532 nm of a nickel metal target in a fast flow tube, with mass spectrometric detection of Ni+ and NiO+. The rate coefficient for the reaction of Ni+ with O3 is k(294 K) = (9.7 ± 2.1) × 10−10 cm3 molecule−1 s−1; the reaction proceeds at the ion-permanent dipole enhanced Langevin capture rate with a predicted T−0.16 dependence. Electronic structure theory calculations were combined with Rice–Ramsperger–Kassel–Markus theory to extrapolate the measured recombination rate coefficients to the temperature and pressure conditions of planetary upper atmospheres. The following low-pressure limiting rate coefficients were obtained for T = 120–400 K and He bath gas (in cm6 molecule−2 s−1, uncertainty ±σ at 180 K): log10(k, Ni+ + N2) = −27.5009 + 1.0667log10(T) − 0.74741(log10(T))2, σ = 29%; log10(k, Ni+ + O2) = −27.8098 + 1.3065log10(T) − 0.81136(log10(T))2, σ = 32%; log10(k, Ni+ + CO2) = −29.805 + 4.2282log10(T) − 1.4303(log10(T))2, σ = 28%; log10(k, Ni+ + H2O) = −24.318 + 0.20448log10(T) − 0.66676(log10(T))2, σ = 28%). Other rate coefficients measured (at 294 K, in cm3 molecule−1 s−1) were: k(NiO+ + O) = (1.7 ± 1.2) × 10−10; k(NiO+ + CO) = (7.4 ± 1.3) × 10−11; k(NiO+ + O3) = (2.7 ± 1.0) × 10−10 with (29 ± 21)% forming Ni+ as opposed to NiO2+; k(NiO2+ + O3) = (2.9 ± 1.4) × 10−10, with (16 ± 9)% forming NiO+ as opposed to ONiO2+; and k(Ni+·N2 + O) = (7 ± 4) × 10−12. The chemistry of Ni+ and NiO+ in the upper atmospheres of Earth and Mars is then discussed.