Ab Initio Calculations of Harmonic Force Constants. III. An Exact Calculation of the H2+ Force Constant

The energy, within the Born–Oppenheimer approximation, of the ${\text{1sσ}}_g$ state of H₂⁺ is evaluated for internuclear separations of 1.90–2.10 a.u. in steps of 0.01. These energies are used to determine the force constant of H₂⁺ in the ${\text{1sσ}}_g$ state; it is found to be 0.102970438 a.u.