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[en] Photodetachment is a fundamental ionization mechanism in which electrons are detached from negative ions following photoabsorption. Cross sections for this process, and the inverse process of radiative attachment, are required in the modeling of low density plasmas such as those found, for example, in certain astrophysical environments. A survey of the field will be presented
[en] Highlights: • A series of hetero-binuclear superhalogen anions has been theoretically studied. • The large VDEs (7.449–8.978 eV) verify the superhalogen identity of these anions. • Two central atoms affect the superhalogen character in different ways. • The extra electron distribution has effect on VDEs of such superhalogen anions. Hetero-binuclear superhalogen anions, namely MM′F4− and MM″F5− (M = Li, Na; M′ = Be, Mg, Ca; M″ = B, Al, Ga), have been theoretically characterized at the MP2(FULL)/6-311+G(3df) level. It is found that two central atoms can be linked by at most three fluorine ligands. The large vertical electron detachment energies (VDEs, 7.449–8.978 eV) verify the superhalogen identity of these anions. The VDEs of both MM′F4− and MM″F5− decrease when the atomic size of M increases whereas increase with the size of M′ and M″. Besides, the extra electron distribution also has effect on the VDEs of such superhalogen anions.
[en] In a plasma containing negative ions, the value of the floating potential of a Langmuir probe is lowered below the corresponding value for an electron-positive ion plasma, the reduction depending on the degree of attachment in the plasma. Hence, a measurement of probe floating potential in an electro-negative plasma can be used to provide a value for the ratio of negative ion to electron number density (degree of attachment) in the plasma. Measurements have been made in the Faraday dark space region of an iodine glow discharge. The principal sources of error are the location of plasma potential, and the extrapolation of the positive ion current region of the probe. Nevertheless, good agreement is obtained between values using the lowering of floating potential technique and more conventional probe methods, thereby providing a useful mutual check in the probe study of plasmas containing large numbers of negative ions. (author)
[en] The temperature dependence of the low-energy electron attachment and autodetachment processes for c-C4F6 in a N2 buffer gas has been studied in the temperature, T, range of 300 to 600 K and the mean electron energy, <ε>, range from 0.19 to 1.0 eV. The low-energy electron attachment rate constant for c-C4F6 shows only a slight dependence on gas temperature. In contrast, the autodetachment frequency increases by more than four orders of magnitude when T is increased from 300 to 600 K. This increase in autodetachment is due to the increase in the internal energy content of the c-C4,F6- anion with increasing T. The autodetachment process under consideration is a heat-activated process and has an activation energy E* of 0.24 eV. Significance of these results to gaseous dielectrics is indicated
[en] The results of spin-asymmetry studies carried out for electron impact ionization of hydrogen revealed significant deviations from the prediction of the Wannier threshold law for double escape. Detailed statistical analyses of four other previously published threshold studies, all of which had originally claimed consistency with the Wannier law, now provide additional evidence for difficulties with the conventional theory. In contrast to the corollary of the ergodic hypothesis that only the asymptotic form of the wave function need be considered for threshold escape, it appears that three-body dynamics must actually be taken into account if the problem is to be described properly. As earlier investigations at LAMPF have shown, double photodetachment of the negative hydrogen ion provides an excellent method for investigating the threshold behavior of two-electron escape. The application of new laser technolgies, combined with substantial improvements in LAMPF operation achieved in recent years, should significantly enhance the accuracy with which such measurement can be made
[en] The diagonalization approximation is used to investigate the resonance states of He and H- respectively near the n = 4 and n = 5 hydrogen thresholds. Computations are carried out for states of 1,3P0 symmetries; energies, total and partial widths of autoionization states of helium and autodetaching states of the negative hydrogen ion are calculated. Comparison is made with experiment and theory. (orig.)
[en] A compact orbital representation of ionization processes is described utilizing the difference of calculated one-particle density matrices. Natural orbital analysis involving this difference density matrix simplifies interpretation of electronic detachment processes and allows differentiation between one-electron transitions and shake-up/shake-off transitions, in which one-electron processes are accompanied by excitation of a second electron into the virtual orbital space.
[en] Para- and ortho-Ps atoms are formed in the photodetachment of positronium negative ion. Since the lifetime against the pair annihilation is much shorter for para-Ps(ns) than for ortho-Ps(ns), the production ratio of para- and ortho-Ps atoms is important for the photodetachment experiments. We have derived the ratio explicitly. (author)