Chemi-ionization reactions

Chemi-ionization reactions producing negative ions also remain possible—e.g.,... 

Theoretical Study of the Gas-Phase Chemi-Ionization Reaction between Uranium and Oxygen Atoms. 

Highly exothermic chemical reactions can give ions as products. Such reactions are called chemi-ionization reactions. When one or more of the reactants are formed by pulsed photolysis, and the ion product(s) are time-resolved with a mass spectrometer, this comprises a FPTRMS experiment. The ions can be extracted by a biased pair of electrodes, one of which has an aperture through which ions pass to enter a quadrupole mass spectrometer. The time resolution of this experiment is superior to FPTRMS experiments between neutrals, since the ion velocities are set by the electrode bias voltage, and the thermal molecular velocity distribution limitation is no longer a factor. With modest electrode bias voltages, the detection time can be as short as 2 /is. 

In addition, Munson et al. (77) showed that under certain conditions N4+ is formed by the chemi-ionization reaction ... 

An interesting finding in the study of Chupka et al. is that the H3 ions are also produced at photon energies below the H2 threshold. This was shown to be due to chemi-ionization reactions... 

Kistiakowsky and Michael [263] found a chemi-ionization reaction... 

The powerful technique of two-photon absorption, which permits limitations of Doppler broadening to be overcome (see Chapter 1), has been used in a study on sodium atoms in which the Stark effect in the 5s 2Si and 4d D and D levels was observed.188 The radiative lifetimes of the S and D Rydberg levels of Na,189 the use of laser-induced resonance fluorescence for the measurement of small concentrations of Na vapour,170 the quenching of Na(32P) and K(42P) by N2, 02, H2, and HaO,171 the chemi-ionization reactions of photoexcited atoms,172 and excitation of the K(42P ) level in collisions with rare-gas atoms173 have been the subjects of recent reports. 

Chemi-ionization reactions of the resonant states appear to form the simplest general category because of the applicability of near-resonance, long-range interaction models, in which the dipole transition moments of the noble gas A A( .9) radiative transition and the reagent photoionization transition determine the reaction cross section. The impact-parameter, linear trajectory form of this model of Watanabe and Katsuura has been applied jq chemi-ionization... 

Chemi-ionization reactions of the excited noble gases at thermal energies can occur by the following channels ... 

Penning and Associative Ionization of Atoms.—Several workers have described chemi-ionization reactions of He with an atom, M, in terms of autoionizing transitions between adiabatic potential curves, V and V, correlating with He + M and He + M respectively. Figure 2 shows schematic curves and transitions, representing the processes ... 

The chemi-ionization reactions of He with other open shell atoms such as Na and Hg show analogous characteristics of strongly bound V potentials, an inverse dependence of ionization cross-section on collision energy and markedly broadmed electron energy spectra. ... 

They found that the intensity of the diatomic ion increased as the second power of pressure and its appearance potential was less by 0.7 to 1.5 eV than the ionization potential of the rare gas in question and, hence, the nature of the reaction was established. Similar chemi-ionization reactions have been observed for a number of systems other than the rare gases. Although chemi-ionization is not an ion-molecule reaction, it has subsequently been studied by a number of mass spectrometrists who were interested in collision reactions of ions, and reports in the literature often contain results on both processes. Consequently, it seems reasonable to include a discussion of the chemi-ionization in this volume. 

In hydrocarbon flame fronts, the concentrations of free radicals and excited species are far above equilibrium values the potential energy of the thermodynamically unstable fuel/oxidizer mixture has suddenly been released and the elements are scrambling to an equilibrium arrangement. Under these conditions, the high radical concentrations permit such chemi-ionization reactions as... 

The chemi-ionization reactions given by Eqs. (35) and (36) were reported and characterized by Fite et al. (Fite and Irving, 1972 Fite et al., 1974) ... 

As a result of the strong binding between U and O, and the low ionization energies of UO and UO2, these reactions are substantially exothermic, by greater than 200 kJ mol and proceed spraitaneously under low-energy conditions. Associative reactions between U and O2 proceed at approximately the collisional rate, but the chemi-ionization processes account for only 1% of the products, with neutral UO-pO as the dominant products. In the case of the reaction of U and O, where no neutral channel is accessible, the chemi-ionization process proceeds with a rate close to the collisional limit. Dyke et al. (1988) studied the chemi-ionization reaction of U with O2 (Eq. 36) and that of U with N2O, Eq. (37), by chemielectron spectroscopy ... 

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