Electron Ion And Ion Ion Dissociative Recombination Of Oxygen

Dissociative Recombination of Molecular Ions with Electrons is a comprehensive collection of refereed papers describing the latest developments in dissociative recombination research. The papers are written by the leading researchers in the field. The topics covered include the use of microwave afterglows, merged beams and storage rings to measure rate coefficients and to identify the products and their yields. The molecules studied range in size from the smallest, H2+, to bovine insulin ions. The theoretical papers cover the important role of Rydberg states and the use of wave packets and quantum defect theory to deduce cross sections, rate constants and quantum yields. Several theoretical and experimental papers address the controversial topic of H3+ dissociative recombination and its importance in the interstellar medium. Dissociative recombination studies of other molecular ions in the interstellar medium and in cometary and planetary atmospheres are covered. Ionization is an important competitive process to dissociative recombination and its competition with predissociation and its role in the reverse process of the association of neutral species is presented. Dissociative attachment, in which an electron attaches to a neutral molecule, has many similarities to dissociative recombination. The topics covered include the accurate calculation of electron affinities, attachment to molecules, clusters, and to species absorbed on solid surfaces and electron scattering by a molecular anion.

Two-body ionospheric reactions involving oxygen and/or nitrogen are briefly reviewed with special emphasis on the temperature dependencies of these reactions and reactions involving excited ions. The temperature dependence of most reactions are fairly well known except for processes which can occur over a wide range of thermospheric temperatures, particularly O and/or O(+) reactions and dissociative recombination processes. Disagreements between laboratory and aeronomically deduced loss processes for O(+) ions are discussed. The absence of laboratory measurements of excited ion reactions at typical E- and F-region temperatures hinders twilight and auroral studies. The lack of knowledge concerning the state of excitation of reaction products impairs airglow and chemical aeronomy studies. The reaction between O(2(+) and NO may be an important source of electronically excited O2 molecules in auroras.

Information obtained from laboratory experiments and theoretical calculations concerning electron ion and ion-ion recombination processes is re viewed. It is concluded that the two-boc esses of dissociative recombination and radia tive recombination between electrons and positive ions and of mutual neutralization of positive and negative ions are of importance for the iono sphere. Laboratory aferglow measurements on ions of ionospheric interest yield values for the dissociative recombination coefficients. Theoretical calculations yield radiative recom bination values for H(), He(), O() ions and electrons of 4-5 x 10 to the -12th power cc/sec at 250 K and a T(sub e) sup-0.5 dependence on electron temperature. Auxiliary processes affect ing ionospheric recombination, such as electron attachment to O2 molecules, charge transfer both for positive ions and negative ions, and ion conversion, are briefly considered. (Author).

Charge transfer and charged rearrangement collision cross sections were measured at energies down to 2 eV with identification of product ions and some state selection of primary ions. Electric impact studies of molecular oxygen with high resolution provided new important information on the ionization process, while investigations of negative ions in afterglows of atmospheric gases demonstrated the comparative lack of understanding in this important aspect of atmospheric deionization. The following reactions were studied by the ionization afterglow technique: ionic recombination in O2; thermalization diffusion and electron-ion dissociative recombination in N2; attachment in gases containing NO2; attachment and electron-ion dissociative recombination in gases containing NO. (Author).

The dissociative recombination of molecular ions with electrons determines many of the properties of the Earth's ionosphere under both quiescent and disturbed conditions. However, in spite of its importance, there has never been an experimental measurement of dissociative recombination rates from individual excited ion vibrational levels. Completed are large scale ab initio calculations of cross sections and rates for the dissociative recombination of the molecular oxygen ion leading to excited oxygen atoms in the lS and ID states, the upper states of the well known green and red lines, respectively. A new method for calculating electronic autoionization widths using high Rydberg state wave functions to represent the inner part of the free electron wave function has been used and tested on the NO molecule where the widths can be calculated to an expected accuracy of about 15%. THe widths have been used to determine dissociative recombination cross sections as a function of electron energy. Large windows have been discovered in the cross sections from excited vibrational levels. The windows, at which the cross sections drop precipitously, are due to the overlap of the peak in the continuum vibrational wave functions.

I was very happy to learn that Plenum Press has decided to publish an English edition of Chemistry of the Ionosphere. Although the book was largely intended for the Soviet reader in order to fill some gaps in Russian-language reviews on aeronomic problems, I hope that it may be useful to foreign specialists engaged in iono spheric research as well. Naturally, during the time which has elapsed since the preparation of the Russian edition new studies have been published in the world literature on the problems dealt with in this book. The most important of these are noted in the ap pendix to this edition, but some problems (for example, with respect to the physics of negative ions in the lower ionosphere) require a radical reexamination, which cannot be done in a brief appendix. I will be pleased if publication of the book in English will as sist in removing some of the currently existing ambiguities in basic problems of upper atmosphere chemistry. A. D. Danilov Preface to the Russian Edition 1 In the last decade surprising successes have been achieved in the study of the earth's upper atmosphere by use of rockets and artificial satellites. These investigations have made it clear that the upper atmosphere (and particularly the ionospheric region at altitudes 100-1000 km) is a considerably more complex formation than could be visualized prior to the advent of active studies with space vehicles.

The kinetic energy distribution of ions produced by a dissociative ionization process is derived, taking into account the effect of thermal motion of the target molecule. In the case of dissociative attachment of monoenergetic electrons to a diatomic molecule the width at half maximum of the negative ion energy distribution is given by sq.rt.(11(Beta)kTE) where Beta is the ratio of the mass of the ion to that of the parent molecule, T is the target gas temperature, and E is the most probable ion energy. Using a crossed field velocity filter O( - ) ion energy distributions arising from the attachment of essentially monoenergetic electrons to O2 are studied as a function of electron energy at two gas temperatures. The measured widths of the distributions are consistent with the above relationship. Measurements of E as a function of the electron energy allow a determination of the electron affinity, A, of atomic oxygen. The result, A = 1.5 plus or minus 0.1 eV, is in excellent agreement with photodetachment threshold determinations. (Author).