title: Ab initio study of the positronation of the CaO and SrO molecules including calculation of annihilation rates.
abstract: Ab initio multireference single- and double-excitation configuration interaction calculations have been performed to compute potential curves for ground and excited states of the CaO and SrO molecules and their positronic complexes, e(+)CaO, and e(+)SrO. The adiabatic dissociation limit for the (2)Σ(+) lowest states of the latter systems consists of the positive metal ion ground state (M(+)) and the OPs complex (e(+)O(-)), although the lowest energy limit is thought to be e(+)M + O. Good agreement is found between the calculated and experimental spectroscopic constants for the neutral diatomics wherever available. The positron affinity of the closed-shell X (1)Σ(+) ground states of both systems is found to lie in the 0.16-0.19 eV range, less than half the corresponding values for the lighter members of the alkaline earth monoxide series, BeO and MgO. Annihilation rates (ARs) have been calculated for all four positronated systems for the first time. The variation with bond distance is generally similar to what has been found earlier for the alkali monoxide series of positronic complexes, falling off gradually from the OPs AR value at their respective dissociation limits. The e(+)SrO system shows some exceptional behavior, however, with its AR value reaching a minimum at a relatively large bond distance and then rising to more than twice the OPs value close to its equilibrium distance.
authors.affiliation: Physikalishe/Theoretische Chemie, Fachbereich C-Mathematik und Naturwissenschaften, Bergische Universität Wuppertal, D-42119 Wuppertal, Germany. buenker@uni-wuppertal.de
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Buenker
authors.forename: Heinz-Peter
authors.initials: HP
authors.lastname: Liebermann