Electron molecular ion recombination: Product excitation and fragmentation

Abstract

Electron-ion dissociative recombination is an important ionization loss process in any ionized gas containing molecular ions. This includes the interstellar medium, circumstellar shells, cometary comae, planetary ionospheres, fusion plasma boundaries, combustion flames, laser plasmas and chemical deposition and etching plasmas. In addition to controlling the ionization density, the process generates many radical species, which can contribute to a parallel neutral chemistry. Techniques used to obtain rate data and product information (flowing afterglows and storage rings) are discussed and recent data are reviewed including diatomic to polyatomic ions and cluster ions. The data are divided into rate coefficients and cross sections, including their temperature/energy dependencies, and quantitative identification of neutral reaction products. The latter involve both ground and electronically excited states and including vibrational excitation. The data from the different techniques are compared and trends in the data are examined. The reactions are considered in terms of the basic mechanisms (direct and indirect processes including tunneling) and recent theoretical developments are discussed. Finally, new techniques are mentioned (for product identification; electrostatic storage rings, including single and double rings; Coulomb explosion) and new ways forward are suggested.

CRITICAL REVIEW OF N, N + , N + 2 , N ++ , And N ++ 2 MAIN PRODUCTION PROCESSES AND REACTIONS OF RELEVANCE TO TITAN'S ATMOSPHERE

“…For reactions between singly charged ions and neutrals, Anicich & McEwan (Anicich 2003McEwan & Anicich 2007;McEwan et al 1998) published several review papers considering all ion-molecule reactions, at room temperature, which can play a role in Titan's atmospheric chemistry. Electron-ion recombination reactions (Adams et al 2006;Florescu-Mitchell & Mitchell 2006;Johnsen 2011;Thomas 2008;Vigren et al 2012) were considered in several recent review papers. For doubly charged ion reactions, Thissen et al (2011) published a recent review which gives a more general overview of this class of reactions and their possible role in planetary atmospheres.…”

Towards a Consistent Chemical Kinetic Model of Electron Beam Irradiation of Humid Air

“…This expectation is confirmed by flowing afterglow (FA) experiments [23]. FA experiments are carried out at pressures much lower than those we seek to model; however, given the large negative reaction enthalpies, collisional deactivation, even at total pressures of 1 atm, would appear unlikely to suppress the dissociation reactions observed in experiment.…”

“…These ideas were necessarily oversimplified in being applied to identify a single product set for each reaction: 1) Reactions of anions with aprotic cations are assumed to proceed by electron transfer to the cation [23], which would be expected to deposit most of the reaction exothermicity in the newly neutralized cation. In this model, the reaction below:…”

The SIFT and FALP techniques; applications to ionic and electronic reactions studies and their evolution to the SIFT-MS and FA-MS analytical methods

“…Electron attachment reactions involving simple and complex neutral species in the gas phase (and to some extent on particle surfaces) are the source of the free negative ions observed by rocket-borne mass spectrometers in these lower atmosphere regions. These complex reaction schemes can be made semi-quantitative using the considerable body of kinetics data provided by the many SIFT [37,99,100] and FALP studies [19,88].…”