On the meaning of “collision rate constants” for ion-molecule reactions: Association of hydrogen atoms with C6H5+ and small alkyl radicals with C7H7+ ions

Old School Techniques with Modern Capabilities: Kinetics Determination of Dynamical Information Such as Barriers, Multiple Entrance Channel Complexes, Product States, Spin Crossings, and Size Effects in Metallic Ion–Molecule Reactions

“…Assuming that an entrance complex may only be formed if the kinetic energy exceeds the centrifugal barrier and because kinetic energy and angular momentum are linked by an impact parameter b , the reaction may occur only up to a maximum separation b max for a given kinetic energy. b max calculated assuming a Maxwell–Boltzmann distribution for kinetic energy (corresponding to a the LGS capture rate constant) is generally ∼5–8 Å; for species physically larger than this value, capture rates must also account for finite size effects …”

“…The apparent supercollisional rate constants, as well as the positive temperature dependences for reactions as efficient as this, led us to question how we were thinking about the collisional limit. Recently we explicitly considered the impact of short-range valence potentials in calculating a collision rate . It was found that inclusion of a “hard sphere” collision term is appropriate when anisotropy in the short-range valence potential does not greatly reduce capture rates, similar to approaches taken in the past. , Armed with this new approach, we fit the observed temperature dependences with an Arrhenius fit, while allowing the pre-exponential factor to include capture incorporating not only the typical LGS collisional limit but also a hard sphere term.…”

“…In this case, a simple analysis solved a decades long interrogation of what caused these odd behaviors, enabled by the experimental upgrades. Finally, for other metal anions reacting with oxygen, finite size effects ,,,, were shown to be important, prompting a look into details of how to incorporate such effects in the cluster reactions. The data for five metals all showed that oxidation was controlled by transfer of an electron to oxygen, akin to what is needed for surface oxidation just as with the Al n – clusters.…”

Proton leap: shuttling of protons onto benzonitrile

“…Its variations have so far been successfully used for analysis of various reactions without barriers, which involve neutral molecules, ions, and radicals. 74–82 Classical capture model 83 developed by Langevin 84 is based on the following assumptions: (i) the reaction rate constant is determined solely by the long-range attraction of the reactants; (ii) ion–molecule collision is reactive if and only if system's kinetic energy is larger than or equal to the height of the centrifugal barrier; (iii) Maxwell–Boltzmann distribution of molecular speeds is attained; (iv) internal degrees of freedom remain unchanged during the course of the reaction (vibrations, rotations and electronic transitions are neglected). Langevin's derivation, describes interaction of a point charge with a point polarizable neutral particle (ion–induced dipole model).…”

Temperature and energy dependences of ion–molecule reactions: Studies inspired by Diethard Böhme

“…Presumably, a hard sphere instead of capture collision makes it more difficult to find the backside position. In coordination with Jürgen Troe we have since looked both at anisotropic effects on capture (Fernandez et al, 2005; Troe et al, 2005) and finite size effects (Ard et al, 2020). We now plan on reexamining at these results with similar theoretical tools.…”