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

The reactions between Ni+(D-2) and O-3, O-2, N-2, 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 O-3 is k(294 K) = (9.7 +/- 2.1) x 10(-10) cm(3) 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 cm(6) molecule(-2) s(-1), uncertainty +/-sigma at 180 K): log(10)(k, Ni+ + N-2) = -27.5009 + 1.0667log(10)(T) - 0.74741(log(10)(T))(2), sigma = 29%; log(10)(k, Ni+ + O-2) = -27.8098 + 1.3065log(10)(T) - 0.81136(log(10)(T))(2), sigma = 32%; log(10)(k, Ni+ + CO2) = -29.805 + 4.2282log(10)(T) - 1.4303(log(10)(T))(2), sigma = 28%; log(10)(k, Ni+ + H2O) = -24.318 + 0.20448log(10)(T) - 0.66676(log(10)(T))(2), sigma = 28%). Other rate coefficients measured (at 294 K, in cm(3) molecule(-1) s(-1)) were: k(NiO+ + O) = (1.7 +/- 1.2) x 10(-10); k(NiO+ + CO) = (7.4 +/- 1.3) x 10(-11); k(NiO+ + O-3) = (2.7 +/- 1.0) x 10(-10) with (29 +/- 21)% forming Ni+ as opposed to NiO2+; k(NiO2+ + O-3) = (2.9 +/- 1.4) x 10(-10), with (16 +/- 9)% forming NiO+ as opposed to ONiO2+; and k(Ni+center dot N-2 + O) = (7 +/- 4) x 10(-12). The chemistry of Ni+ and NiO+ in the upper atmospheres of Earth and Mars is then discussed.