Positive ion reactions

Abstract

Progress over the past five years in the measurement of rate coefficients and cross sections for interactions between positive ions and neutral niolecules of particular interest to aeronomy is reviewed. Emphasis is placed on the methods of experimentation developed for studies in the range of thernial energies and slightly above. Along with discussion of the range of applicability of each of the techniques, illustrated by examples of nieasurenients on processes of aeronomic interest, some evaluation of limitations of applicability and reliability of the nieasurernents is made. A table surnrnarizing results obtained to date on processes pertaining to the atmospheres of the earth and neighboring planets is presented.Canadian Journal of Chemistry, 47, 1797 (1969) Introductionreactants being in excited states are assessed, and Five years ago at the symposium preceding the present one, two reports summarized experimental work on collisions between ions and neutral atomic systems of interest to aeronomy. Paulson (1) reviewed the situation with regard to experiments at thermal and low energies and the present author summarized experiments where the relative energy was sufficiently high that ion beam methods were employed (2). At that time the higher energy techniques were well established and a number of results had been obtained; however, to apply the results to problems of low energies, extrapolation by rather unreliable means had to be employed. In only a few cases were thermal and low energy data available since the techniques of experimenting at these low energies were in a very early stage of development.The five years intervening between these symposia has seen the situation reverse itself. The development of low energy experimental methods has been rapid and the amount of low energy data on the principal atmospheric species is now quite large. To an ever-increasing extent, the role of the higher energy experiments is to examine details of reactions in order to better interpret the lower energy results as they apply to the atmosphere and to discover processes deserving of attention in thermal energy experiments.Accordingly, it is appropriate here to review the principal laboratory methods now in use to obtain thermal energy data on total cross sections and reaction rate coefficients for ion-neutral reactions, to examine briefly the modifications of these methods and alternative methods by which the effects of increased kinetic energy and

The airborne mass spectrometer AIMS – Part 1: AIMS-H<sub>2</sub>O for UTLS water vapor measurements

“…These reactions are described by, e.g., Fite (1969), Fehsenfeld et al (1971) and Ferguson (1974). Due to the rapid transfer of charge from N + 2 to O 2 , the majority of positive ions entering the drift region are O + 2 ions.…”

Steady-state kinetic treatment of the emission from reduced pressure microwave induced discharges in helium

“…Similarly, the average excitation cross-section is ( gj ) = Jcz 01 (t)P(t)dc (9) T h e Electron Energy Distribution P(e). Assuming the time dependence of the electric field in the discharge to be of the form E = Eo cos 2 n v t , at steady-state, we may, following Fite (14), equate the rate of energy loss of an electron in elastic collisions with helium atoms to the power, averaged over a cycle, delivered to an electron by the field. The neglect of inelastic collisions (i.e., excitation processes) will not lead to serious error because the cross-sections of the excitation These values were obtained by using Equations 11 and 12. processes (13) are of the order of times smaller than those of the elastic collisions (15).…”

Theoretical models of ionospheric storms

“…Rate coefficients of the reactions which are of importance in the upper atmosphere have been progressively studied by laboratory experiments and the experimental results have recently been summarized by Biondi (1969) for recombination processes and by Fite (1969) and Ferguson (1969) for positive ion-molecule reactions.…”