Homonuclear associative ionization

Homonuclear associative ionization) (1) (Heteronuclear associative ionization) (2)... 

An analogous reaction in rubidium suffices to explain the observations of Lawrence and Edlefsen. Subsequent investigations by Mohler and Boeckner and Freudenberg were consistent with the occurrence of (11), a homonuclear associative ionization reaction. 

MODERN EXPERIMENTAL STUDIES 3.1. Homonuclear Associative Ionization... 

Utilizing the continuous mass spectrometric techniques developed by Arnot and co-workers and Hornbeck and Molnar in which reaction identification is made from considerations of the appearance potentials of the product ions and from the effects of electron energy, pressure, and repeller potential on product-ion intensity, homonuclear associative ionization reactions have been reported in helium, " in neon, "- " " i46A9,5o,52-si,62) krypton,< " " - " > in... 

The existence of the homonuclear associative ionization reaction in nitrogen seems to be well established/ although it should be pointed out that somewhat earlier, Saporoschenko had observed an appearance potential for N4 of 15.8 eV and had concluded from this and from the pressure dependence that the process forming N4 was... 

Homonuclear associative ionization reactions have also been observed in studies in which the ionic abundances in gas discharges are determined mass spectrometrically as functions of pressure, discharge current, and gas composition. Reaction identification is difficult in such studies because of the complexity of the multitude of excitation, ionization, neutralization, and radiative processes occurring simultaneously. Nevertheless homonuclear associative ionization reactions have been reported in dc discharges in helium, neon, 63-65) argon, 65-68) krypton, and xenon. Associative ionization reactions have also been reported in rf discharges in helium, argon, and xenon. ... 

Photoionization studies without mass analysis (similar in principle to the first studies of homonuclear associative ionization) have recently been conducted in argon, krypton, xenon, sodium, potassium, rubidium, and cesium. The apparatus used by Huffman and Katayama is depicted in Fig. 5. The ion current reaching the collector plate and the radiation intensity incident on the photomultiplier are measured as a function of wavelength of incident radiation (from a monochromator) and pressure of gas in the cell. For purpose of reaction identification, this method is of value only in the pure gases, in which there... 

In Table II are shown the lowest ionization potentials of the neutral atoms and molecules in Table I, along with the energies and identities of the metastable states. Comparison of the appearance potentials in Table I with the data in Table II makes very clear the fact that homonuclear associative ionization does not involve the long-lived metastable states. Indeed, the lowest-energy states capable of homonuclear associative ioniza-... 

In this set of elementary reactions, k,-, k, and k represent the specific reaction rates for electron-impact excitation, electron-impact ionization, homonuclear associative ionization, and radiative decay of the reactive state X to an unreactive one X respectively. It is assumed in the treatment that only one excited state is involved. 

For the cases of Ar2, Kr2, and Xe2 formation, Huffman and Katayama have shown that all optically accessible excited states whose energies lie above the threshold energy undergo homonuclear associative ionization. It would seem highly likely that the same statement would apply also to all optically forbidden states above threshold. Therefore, the electron-impact ionization-efficiency curves must be a superposition (weighted with respect to excitation cross sections) of the excitation functions of all excited states above threshold. 

TABLE III. Effective Radiative Lifetimes for Homonuclear Associative Ionization in Helium and Argon... 

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