Energy dependence of the rate constant of the reaction N++NO at collision energies 0.04 to 2.5 eV

Surprising behaviors in the temperature dependent kinetics of diatomic interhalogens with anions and cations

Rate constants and product branching fractions of reactions between diatomic interhalogens (ICl, ClF) and a series of anions (Br^-, I^-) and cations (Ar⁺, N₂⁺) are measured using a selected ion flow tube apparatus and reported over the temperature range 200-500 K. The efficiency of both anion reactions with ICl is 2%-3% at 300 K to yield Cl^-, increasing with temperature in a manner consistent with the small endothermicities of the reactions. The anion reactions with ClF are 10%-20% efficient at 300 K to yield Cl^- and also show a positive temperature dependence despite being highly exothermic. The stationary points along the anion + ClF reaction coordinates were calculated using density functional theory, showing no endothermic barriers inhibiting reaction. The observed temperature dependence can be rationalized by a decreasing dipole attraction with increasing rotational energy, but confirmation requires trajectory calculations of the systems. All four cation reactions are fairly efficient at 300 K with small positive temperature dependences, despite large exothermicities to charge transfer. Three of the four reactions proceed exclusively by dissociative charge transfer to yield Cl⁺. The N₂⁺ + ClF reaction proceeds by both non-dissociative and dissociative charge transfer, with the non-dissociative channel surprisingly increasing with increasing temperature. The origins of these behaviors are not clear and are discussed within the framework of charge-transfer reactions.

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.

Reactions of N+, N2+, and N3+ with NO from 300 to 1400 K

Rate constants have been measured from 300 to 1400 K in a selected ion flow tube (SIFT) and a high temperature flowing afterglow for the reactions of N+, N2+ and N3+ with NO. In all of the systems, the rate constants are substantially less than the collision rate constant. Comparing the high temperature results to kinetics studies as a function of translational energy show that all types of energy (translational, rotational, and vibrational) affect the reactivity approximately equally for all three ions. Branching ratios have also been measured at 300 and 500 K in a SIFT for the N+ and N3+ reactions. An increase in the N2+ product at the expense of NO+ nondissociative charge transfer product occurs at 500 K with N+. The branching ratios for the reaction of N3+ with NO have also been measured in the SIFT, showing that only nondissociative charge transfer giving NO+ occurs up to 500 K. The current results are discussed in the context of the many previous studies of these ions in the literature.