The electronic structure and positron annihilation characteristics of positronium halides, [X−; e+]. I. Hartree–Fock calculations and stability

Abstract

The electronic structure of the atom/positron systems [F−;e+], [Cl−;e+], [Br−;e+], and [I−;e+] are examined by means of restricted Hartree–Fock calculations on the ...ns2np6(nl)+, 2L and...ns2np5 (n+1) sls+, 2P,4P states. A modified version of the numerical MCHF72 program of Froese–Fischer was used in these calculations. Our theoretical investigations suggest that...ns2np61s+, 2S is the ground state of the system. It is shown that X− ions have a substantial positron affinity (e.g. ∼5 eV for F− to 3.3 eV for I−) and arguments based on pair-correlation and many-electron perturbation theory are used to obtain hard lower limit estimates of the binding energy of Ps to the X atom. We thus find that the ground state of [X−:e+] is stable with respect to dissociation into X and Ps with binding energies of at least 1.66, 0.80, 0.19, and −0.45 eV for [F−:e+], [Cl−:e+], [Br−:e+], and [I−:e+], respectively. The details of the positronic orbitals are presented and discussed.