Perturbation Calculation of the Energy of the First Excited State (2pσ) of H2+

Abstract

The electronic energy of the 2pσ state of H₂⁺ is calculated by perturbation theory to third order using the Guillemin—Zener wavefunction as a zeroth‐order function. The results agree quite well with the exact calculations except for small internuclear distances, as expected.