Isoelectronic molecules: The 13 and 22 electron sequences of diatomics

A theory of isoelectronic molecules [J. Chem. Phys. 74, 1840 (1981)] has been applied to the ground state of an even (22) electron and an odd (13) electron sequence of diatomics. Each of these is compared to the 14 electron sequence which had been studied previously. In the first instance, a striking correspondence in the dissociation energy De(Z,Z′), bond distance R(Z,Z′), and force constant E(2)(Z,Z′) surfaces for isovalent molecules from the 14 and 22 electron systems has become apparent. For the second, gross differences which arise in these surfaces when one electron is removed from 14 electron molecules are explicable in terms of the nature of the electron-pair bond as opposed to the one-electron bond. A stability rule which excludes ions with charges greater than plus or minus two units is found to hold for these sequences as well as the 14 electron one.