Ab initio configuration-interaction calculations on ground-state Ne2, the excited Σu,g+1,3 and 1,3Πu,g states of Ne2 formed from Ne(3s; 1,3P) and Ne(1S), and the Σu,g+2 and 2Πu,g states of Ne2+ have been carried out. The dissociation energies of the Σu+1,3 excited states of Ne2 were found to be considerably smaller than that of the corresponding molecular ion. Potential maxima were found in the attractive interactions of the excited Ne2 molecule. A semiempirical model, based on the observed atomic splittings, is given for treatment of spin-orbit coupling effects. The adiabatic potential curves resulting from diagonalization of the spin-orbit interaction were found essential to the understanding of spectroscopic observations. Estimates of the long-range dispersion interactions are also presented.

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This article describes the capture of heavy negative particles (µ − , π − , K − , p) by normal atoms, ions and molecules to form exotic systems. Capture by even the hydrogen atom presents great challenges for theoretical treatment. The wide variety of methods used are reviewed, including perturbative, two-state adiabatic and diabatic, time-independent quantum mechanical, timedependent semiclassical and quantum mechanical and quasi-classical treatments. A few of these methods, as well as the Fermi-Teller model, have also been applied to heavier atomic targets. Most of the methods, other than the quasi-classical formulations, are not yet up to treating the dynamical electron correlation and multiple ionization found to be important in capture by multi-electron atoms, or the vibronic coupling found to be important in capture by simple molecules. The essential elements of potentially more rigorous quantum mechanical theories are characterized. The experimental data on capture states and relative capture probabilities in mixtures are also discussed. The connection of this experimental data to the theoretical capture calculations is fairly tenuous, but forthcoming experiments with antiprotons promise direct tests of some of the recent theoretical findings.

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Antiproton (p ) and negative muon ( Ϫ ) captures by helium and neon atoms are treated using the fermionmolecular-dynamics method, yielding capture cross sections, initial quantum numbers, and ejected-electron energies. The calculated angular-momentum distributions tend to pile up at lϭnϪ1 and are not well fitted by the form (2lϩ1)e ␣l , which is often assumed in experimental analyses. The residual electrons are generally left in a ''shake-up'' state. When capture is accompanied by multiple ionization, the second and later electrons escape with increasing kinetic energies, a process that is not well described as quasiadiabatic. In a 50:50 mixture of helium and neon, the calculated Ne:He capture ratios are 3.36 for p and 3.69 for Ϫ . The Ϫ per-atom capture probability is almost independent of the neon fraction and is in overall agreement with several Ϫ and Ϫ experiments; for p there is a rather strong dependence on neon fraction, but there are as yet no experiments. The possible experimental indication of a strong isotope effect on capture of Ϫ in mixtures of 3 He and 4 He is not supported by the present calculation. PACS number͑s͒: 36.10.Ϫk, 34.10.ϩx, 25.43.ϩt, 03.65.Sq p capture by the hydrogen atom using the new antiproton decelerator ͑AD͒ at CERN.

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The classical-trajectory Monte Carlo method has been used to determine ionization and capture cross sections and stopping powers for collisions of negative muons with hydrogen atoms. The calculations were done for muon energies from about 3 eV to 150 keV. The uncertainty in the results is thought to be about 30%. Most muons are found to be captured in collisions at energies below the ionization potential of the target atom.

Ne~experimental results on muon-catalyzed d-t fusion are reported. Unexpected target-density effects have been discovered both in dt p, molecular formation in t p, + 02 collisions and in the effective sticking probability. The dt p. formation rate is significantly enhanced at high density, presumably because of a strong three-body contribution. The origin of the observed reduction of the sticking probability at high density remains unclear. Both effects increase the number of fusions per muon that can be achieved; 150+ 4(stat.) + 20(syst.) fusions per muon have been observed.