Diagrammatic perturbation theory: Potential curves for the ground state of the carbon monoxide molecule

Diagrammatic many‐body perturbation theory is used to calculate the potential energy function for the X 1 σ+ state of the CO molecule near the equilibrium nuclear configuration. Spectroscopic constants are derived from a number of curves which are obtained from calculations taken through third order in the energy. By forming [2/1] Padé approximants to the constants we obtain: r e = 1.125 Å (1.128 Å), B e = 1.943 cm −1 (1.9312 cm −1 ), a B e = 0.0156 cm −1 (0.0175 cm −1 ), W e = 2247 cm −1 (2170 cm −1 ), W e X e = 12.16 cm −1 (13.29 cm −1 ), where the experimental values are given in parenthesis.