Polarized Electrons 2nd Edition 12 Atomic Spectra By J. Kessler and Radiative Transitions 2nd Edition By I. I. Sobel' man 2 Multiphoton Processes Multiphoton Processes in Atoms Editors: P. Lambropoulos and S. J. Smith 13 By N. B. Delone and V. P. Krainov 3 Atomic Many-Body Theory Atoms in Plasmas 2nd Edition 14 By I. Lindgren and J. Morrison By V. S. Lisitsa 4 Elementary Processes 15 Excitation of Atoms in Hydrogen-Helium Plasmas and Broadening of Spectral Lines Cross Sections 2nd Edition and Reaction Rate Coefficients By I. I. Sobel'man, L. Vainshtein,

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We present the results of an experimental study of magnetic dipole (M1) transitions in highly charged argon ions (Ar X, Ar XI, Ar XIV, Ar XV) in the visible spectral range using an electron beam ion trap. Their wavelengths were determined with, for highly charged ions, unprecedented accuracy up to the sub-ppm level and compared with theoretical calculations. The QED contributions, calculated in this Letter, are found to be 4 orders of magnitude larger than the experimental error and are absolutely indispensable to bring theory and experiment to a good agreement. This method shows great potential for the study of QED effects in relativistic few-electron systems.

Absolute detection efficiencies for singly and multiply charged positive ions have been measured for a channelplate and for two different channel electron multipliers (CEM). The efficiencies were measured for impact energies between approximately 0.25 and 25 keV and for ion masses ranging from 14 to 132. The maximum efficiencies were found to be the same for all ions investigated and were approximately 58% for a channelplate and 89% for the CEMs. For a channelplate it is shown that the detection efficiencies for heavier ions scale to a single curve if plotted versus the impact energy divided by the square root of the ion mass. Data taken from the literature imply that lighter ions scale differently. Polynomial fitting parameters to the present efficiency curves are provided.

Singly, doubly and triply differential information, obtained from coincidence measurements, are presented for 250 eV positron and electron impact ionization of molecular nitrogen. Comparisons of these data as functions of energy loss, scattering, and emission angles illustrate differences associated with the sign of the projectile charge. Via a deconvolution and normalization procedure, the triply differential data are converted to absolute cross sections. By fitting the triply differential cross sections for single ionization with simple functions, the intensities, directions, and peak to background intensities of the binary peaks, plus the ratio of recoil to binary interactions, are compared for positron and electron impact. Formulae for the binary and recoil intensities plus for the orientation of the binary peak as a function of momentum transfer are extracted from the data. Differences in the relative amount of fragmentation as a function of energy loss are also observed.