Branching ratios for electronically excited oxygen atoms formed in the reaction of N+ with O2 at 300 K

Reexamination of ionospheric chemistry: high temperature kinetics, internal energy dependences, unusual isomers, and corrections

A number of aspects of ionospheric chemistry are revisited. The review discusses in detail only work performed at AFRL, but other work is mentioned. A large portion of the paper discusses measurements of the kinetics of upper ionospheric reactions at very high temperatures, i.e. the upper temperature range has been extended to at least 1400 K and in some cases to 1800 K. These temperatures are high enough to excite vibrations in O2, N2, and NO and comparing them to drift tube data allows information on the rotational temperature and vibrational level dependences to be derived. Rotational and translational energy are equivalent in controlling the kinetics in most reactions. Vibrational energy in O2 and N2 is often found to promote reactivity which is shown to cause ionospheric density depletions. NO vibrations do not significantly affect the reactivity. In a number of cases, detailed calculations accompanied the experimental studies and elucidated details of the mechanisms. Kinetics of two peroxide isomers important in the lower ionospheric have been measured for the first time, i.e. NOO+ and ONOO-. Finally, two examples are shown where errors in previous data are corrected.

A Study of the Reaction of N+ with O2: Experimental Quantification of NO+(a 3∑+) Production (298−500 K) and Computational Study of the Overall Reaction Pathways

The product branching ratios for NO+(X 1Sigma+) and NO+(a 3Sigma+) produced from the reaction of N+ with O2 have been measured at 298 and 500 K in a selected ion flow tube. Approximately 0.5% of the total products are in NO+(a) at both temperatures, despite the fact that the reaction to form NO+(a) is 0.3 eV exothermic. High-level ab initio calculations of the potential energy surfaces for the N+ + O2 reaction show that the reaction from N+(3P) + O2(3Sigma(g)) reactants starts with an efficient early stage charge transfer to the N(2D) + O2+(X 2Pi) channel, which gives rise to the O2+(X 2Pi) product and, at the same time, serves as the starting point for all of the reaction channels leading to NO+ and O+ products. Pathways to produce NO+(a 3Sigma+) are found to be less favorable than pathways leading to the major product NO+(X 1Sigma+). Production of N(2D) has implications for the concentration of NO in the mesosphere.

A Personal history of the early development of the flowing afterglow technique for ion-molecule reaction studies

A personal perspective of the historical development of the flowing afterglow (FA) technique for measuring thermal energy ion-molecule reaction rate constants is presented. The technique was developed in the period starting in late 1962 in what was then the National Bureau of Standards in Boulder, Colorado. The motivation was primarily to obtain a quantitative understanding of the ion chemistry of the terrestrial ionosphere, a program that was substantially achieved. The thermal energy measurements were extended in temperature from 300 K to a range of 80 K-900 K and subsequently to a center-of-mass kinetic energy range up to ∼ 2 eV with the introduction of a drift tube into the FA.The chemical versatility, in regard to both the ion and the neutral reactants measured, remains unequaled and FA systems are currently in widespread use around the world for a variety of chemical research programs.