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Formation and subsequent decay of very highly charged states of CO molecular ions has been studied in 97 MeV collisions between F8+ and CO using a crossed beams apparatus by measuring the energy distributions of carbon and oxygen ions. The kinetic energies released (KER) upon dissociation of COq+ (q=2-10) ions have been investigated by means of large scale, ab initio configuration interaction molecular orbital calculations. Results indicate that dissociation via non-Coulombic potential energy curves of COq+ ions yields lower values of KER than would be expected from purely Coulombic considerations due to the significance of electronic charge density distributions in the internuclear region.

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Potential-energy curves of various electronic states of CO + and CO+ are computed using allelectron ab initio molecular-orbital methods. Configuration-interaction eR'ects are treated by perturbative techniques (using Moiler-Plesset perturbation theory to fourth order) and by variational methods (using the coupled-cluster approach). In the case of CO +, calculations indicate that the lowest-energy II and E+ states are nearly degenerate in the Franck-Condon region but that only the latter is likely to be metastable; the former is expected to predissociate rapidly due to a curve crossing with a purely repulsive E state. Experimental measurements have been carried out on the kinetic energy released when metastable CO + ions dissociate by a tunneling mechanism, using an ion-translational-energy spectrometer. The kinetic-energy spectra are measured of fragment ions produced when CO + dissociates via an intermediate highly excited (dissociative) CO+' state populated in an electron-capture reaction in collision with He. The experimental results remain di%cult to interpret within the framework of the computed potential-energy curves.PACS number(s): 31.20.Ej, 34.50.Gb, 35.20.Gs

Although many studies have been made on the nonmagnetic heavy fermion CePtSi belonging to the o.-ThSi2 structure, to the best of our knowledge no studies have been reported in the other rare-earth members of this series. In this paper, we report our resistivity, magnetization, and heat capacity studies on NdPtSi and SmPtSi. We have established bulk antiferromagnetic ordering in NdPtSi below 3.8 K and ferromagnetic ordering in SmPtSi below 15 K. The heat-capacity studies show large contribution from the crystal-field effects. We have also established bulk superconductivity below 3.8 K in LaPtSi from resistivity, susceptibility, and heat capacity studies. A detailed study