Ab Initio Predictions for Very Small Ions

Abstract

Approximate ab initio calculations are made on all polyatomic unipositive ions with fewer than six electrons. Predictions are made regarding the stability of such ions. For those which are stable, estimates are made of binding energies, geometries, vibration frequencies, and center of charge. The wavefunctions are valence‐bond configuration‐interaction functions built form Gaussian orbitals. All possible valence‐bond configurations within our chosen basis are used in order to eliminate a serious prejudice regarding geometry. BeH₂⁺, LiHeH⁺, He₃⁺, LiH₃⁺, LiH₂⁺, He₂H⁺, HeH₃⁺, H₅⁺, HeH₂⁺, H₄⁺, and H₃⁺ are found to be stable. (More accurate calculations on H₄⁺ show that this ion is not stable relative to H₃⁺ and H.) He₂H₂⁺, HeH₄⁺, and H₆⁺ are found to be unstable. Two stable isomers of BeH₂⁺ are found: a stable triangular form and a metastable linear form. A semiclassical model is used to interpret and extrapolate our results.