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Starting in the 1960s, flow tube apparatuses have played a central role in the study of ion‐molecule kinetics, allowing for immense chemical diversity of cationic, anionic, and neutral reactants. Here, we review studies of oxygen allotropes, excluding ground state O2 (X 3 ∑ g − ${X}^{3}{\sum }_{g}^{-}$), and focusing instead on reactions of cations, anions, and metal chemi‐ionization reactions with ground state atomic oxygen (O 3P), vibrationally excited molecular oxygen (O2(v)), electronically excited molecular oxygen (O2 (a 1 Δ g ${a}^{1}{{\rm{\Delta }}}_{g}$)), and ozone (O3). Historical outlines of work over several decades are given along with a focus on more recent work by our group at the Air Force Research Laboratory. [ABSTRACT FROM AUTHOR]

Rate constants for the dissociation of OH-(H2O) and OH-(H2O)2 by transfer of electronic energy from O2(a1Δg) were measured. Values of 1.8×10-11 and 2.2×10-11 cm3 molecule-1 s-1, respectively, at 300 K were derived and temperature dependences were obtained from 300 to 500 K for OH-(H2O) and from 300 to 400 K for OH-(H2O)2. Dissociative excitation transfer with OH-(H2O) is slightly endothermic and the reaction appears to have a positive temperature dependence, but barely outside the uncertainty range. In contrast, the reaction of OH-(H2O)2 is exothermic and appears to have a negative temperature dependence. The rate constants are analyzed in terms of unimolecular rate theory, which suggests that the dissociation is prompt and is not affected by collisions with the helium buffer gas. [ABSTRACT FROM AUTHOR]

The direct comparison of the reactivity and mechanistic pathways for anionic systems in the gas phase and in solution are described. The reaction of cyanide ion with ethyl iodide has occurred by an [S.sub.N]2 mechanism in solution and primarily by an [S.sub.N]2 mechanism in the gas phase, where 1% of the gas phase reaction is attributed to an elimination process.

A tandem flowing afterglow-selected ion flow tube instrument was used to measure the reaction rate constants and deuterium kinetic isotope effects for the reactions of BrO- with RCl (R = methyl, ethyl, isopropyl, and tert-butyl). The results provide qualitative insight into the competition between two classical organic mechanisms, nucleophilic substitution ([S.sub.N]2) due to solvent effect and base-induced elimination (E2).

The isotopic studies of the carbene anions that could act as prototypical anions and undergo proton transfer and substitution reactions with chloromethanes are reported. The product ion isotope distributions for the reaction of CHCl*(-) with CH[Cl.sub.3] provide insight into the occurrence of an insertion-elimination mechanism, analogous to neutral carbene processes.

The 351.1 nm photoelectron spectra of the N-methyl-5-pyrazolide anion and the N-methyl-5-imidazolide anion are reported. The excellent agreement is found with the calculated FC factors for the N-methyl-5-pyrazolyl radical.

The gas-phase reactions of F–(DMSO),F–(CH3CN), and F–(C6H6) with t-butyl halides wereinvestigated. Reactionrate constants, kinetic isotope effects, and product ion branchingratios were measured using the flowing afterglow selected ion flowtube technique (FA-SIFT). Additionally, the structure of F–(DMSO) was investigated both computationally and experimentally,and two stable isomers were identified. The reactions generally proceedby elimination mechanisms; however, the reaction of F–(C6H6) with t-butyl chlorideoccurs by a switching mechanism. These reactions are compared to previousstudies of microsolvated reactions of t-butyl halideswhere the solvent molecules were polar, protic molecules. [ABSTRACT FROM AUTHOR]

The kinetics for conversion of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. has been investigated as a function of temperature from 150 to 400 K. In contrast to previous studies, which show that the conversion goes completely through a reaction of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., the present results show that Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. plays an increasing role in the conversion as the temperature is lowered. Rate constants are derived for the clustering of H2O to Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and the reactions of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. with H2O to form Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., respectively. In addition, thermal dissociation of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. to lose HNO2 was also found to be important. The rate constants for the clustering increase substantially with the lowering of the temperature. Flux calculations show that Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed.accounts for over 99% of the conversion at 150 K and even 20% at 300 K, although it is too small to be detectable. The experimental data are complimented by modeling of the falloff curves for the clustering reactions. The modeling shows that, for many of the conditions, the data correspond to the falloff regime of third body association. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of eighteen positive ions with chlorine azide (ClN3) have been studied using a selected ion flow tube (SIFT). These measurements allowed for the estimation of both the ionization energy, >930kJmol−1 (>9.6eV), and the proton affinity, 713±41kJmol−1, of chlorine azide. Reaction rate constants have been determined. Product ions have been identified, and quantified when synthetic complications allowed. In addition, general reaction trends have been observed. A reaction coordinate diagram for the novel reaction of N+ with ClN3 is discussed. [Copyright &y& Elsevier]

Abstract: The competition between substitution (SN2) and elimination (E2) has been studied for the reactions of methyl, ethyl, isopropyl, and tert-butyl iodide with Cl−, CN−, and HS− in the gas phase. Previous studies have shown a dominance of the SN2 mechanism for sulfur anions and for some cyanide–alkyl iodide reactions. Although our results support this conclusion for the reactions studied, they reveal that competition between the SN2 and E2 pathways exists for the isopropyl reactions. Steric and electronic effects, upon alkyl group substitution, produce looser and less stable SN2 transition states, however, they can favor the E2 process. These opposing effects on barrier heights produce E2/SN2 competition as steric hindrance increases around the α-carbon, however the relative differences in intrinsic barrier heights lead to significantly different branching ratios. This interpretation is discussed in terms of reaction efficiencies, kinetic isotope effects, linear basicity–reactivity relationships, electrostatic models, and transition state looseness parameters. [Copyright &y& Elsevier]