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The production of lepton tridents by neutrinos in a Coulomb field i s a sensitive test of the diagonal t e r m s in weak-interaction theory. If a charged vector boson exists then it can participate in such reactions as a virtual particle o r a real one if the incident beam energy i s sufficiently high. A neutral vector boson with no magnetic moment cannot interact with the electromagnetic field; s o it participates only a s a virtual particle. We examine in this paper two different effects due to these bosons. F i r s t that they have different effective couplings which modify the V-A interaction to a more general combination of vector and axial-vector currents. At this level changes in the over-all coupling strength a r e more important than retaining effects due to the virtual-boson propagators. The recent model of Weinberg belongs to this classification. Second, we investigate the propagator effect of a charged vector boson mediating the usual V -A theory.

A systematic study of the electronic structure and chemical binding in the dimer ion sequence, Ne2+, Ar2+, Kr+2, and Xe2+, has been carried out using density functional methods. For comparison, ab initio configuration-interaction calculations were also performed for the Ar2+ ion. These studies include detailed calculations of the pertinent potential energy curves and an analysis of the calculated spectroscopic properties of the bound states of these ions. A regular progression is found in the spectroscopic properties for the ground A 2Σ+1/2u state which leads to some remarkably simple conclusions concerning the nature of the binding and the size of these dimer ions. For the heavier systems, Kr2+ and Xe+2, spin–orbit coupling becomes important, resulting in a strong mixture of the Λ–S coupled Σ and Π states. This mixing affects the strength of the binding in the ground state. A comparison with other ab initio studies and an analysis of the asymptotic behavior at large internuclear separations is given. These dimer ion species illustrate the classic Hartree–Fock symmetry dilemma arising from improper dissociation character. The nature of this problem for ionized homopolar species is discussed.

Rate constants have been measured for the reactions of O Ϫ with CH 4 , CH 2 D 2 , and CD 4 as a function of ion-neutral average center-of-mass kinetic energy, ͗KE cm ͘, at several temperatures over the range 93 K-565 K using a selected ion flow drift tube apparatus. For the CH 4 reaction we also report measurements made using a high-temperature flowing afterglow ͑HTFA͒ instrument over the temperature range 300 K-1313 K. The rate constants are found to have a very large isotope effect, with the CH 4 rate constant a factor of 15 higher than the CD 4 rate constant at 93 K. The rate constants generally have a minimum with respect to temperature and ͗KE cm ͘, except for the higher-temperature data for CD 4 where the rate constants show only an increase with increasing kinetic energy. The data indicate that increasing rotational temperature decreases the rate constants and that rotational energy behaves similarly to translational energy. Single excitations of bending and twisting vibrations have a negligible effect on the rate constant. Either the stretching vibrations or overtones of the bending vibrations increase the rate constants. If the stretches are responsible for the increase in the rate constants, the derived rate constant for a single quantum of stretch excitation (vϭ1) is 5ϫ10 Ϫ10 cm 3 s Ϫ1 , a factor of 6 larger than the rate constant for vϭ0. The CH 2 D 2 rate constants are approximately equal to the averages of the rate constants for the pure isotopes. The product branching ratio (OH Ϫ /OD Ϫ ) shows no dependence on CH 2 D 2 rotational temperature or low-frequency CH 2 D 2 vibrations. A theoretical study of the minimum energy reaction path was performed to help elucidate the reaction dynamics. The minimum energy reaction surface was characteristic of the standard double minimum pathway for ion molecule reactions. The height of the central barrier was found to be close to the energy of the reactants and varied with isotopic substitution. Conformationally different transition states are found for these isotopic reactions. Theoretical studies at the QCISD͑T͒ level of theory find distinct transition states corresponding to O Ϫ ϩCH 4 , O Ϫ ϩH-CHD 2 , O Ϫ ϩD-CH 2 D, O Ϫ ϩCD 4 . The transition state barriers increase in the order O Ϫ ϩCH 4 , O Ϫ ϩH-CHD 2 , O Ϫ ϩD-CH 2 D, and O Ϫ ϩCD 4 , in agreement with experimental reaction rates. The main features of the reactivity are explained by the characteristics of the reaction surface.

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