A Half Bond and a single Bond Formed from 1s Electron

Abstract

We discuss a half bond and a single bond formed from 1s electron of H₂⁺, H₂, HeH⁺, He₂⁺,and He₂²⁺ using UMP2 with 6–311++G** basis set. Equilibrium nuclear distances of H₂⁺, H₂, HeH⁺, He₂⁺,and He₂²⁺ are 1.050, 0.738, 0.785, 1.086, 0.712 Å (1 Å =1⁻¹⁰m) respectively The difference of the nuclear distances is explained by electron repulsion and orbital correlation. The nuclear distance of He₂⁺ is shorter than that of H₂⁺ but longer than that of He₂²⁺. As to the possible cause it is possible to consider that the 1s orbital radius of He₂⁺ is shorter than that of H₂⁺ or that a 3^rd electron occupied the anti-bonding orbital of He₂²⁺.