Relativistic Theory of H2+

The Dirac equation for H₂⁺ is reduced to a form similar to that of the Schrödinger equation with some perturbation terms. A first‐order perturbation calculation for the ${\text{1sσ}}_g$ state then reveals that these relativistic effects lower the electronic energy by a small amount of order ${\text{0.2α}}^2$ for most internuclear separations and thereby make the molecule slightly more stable. The formalism is readily generalized to the isoelectronic sequence of H₂⁺, and the ratio of the relativistic correction to the nonrelativistic energy is found to be of order $Z^2{\alpha }^2$ . Consequently, the relativistic correction becomes progressively more important as $Z$ increases.