Ab Initio Calculations on 62 Low‐Lying States of the O₂ Molecule

Ab initio calculations have been made on the 62 low‐lying states of molecular O₂ which result from the combination of O atoms in $P3$⁠, $D1$⁠, and $S1$ atomic states. The calculations are done at nine different internuclear separations, and potential‐energy curves are presented for all states. Twelve bound states were found: the lowest seven have been observed; two others have been predicted before; three are new. The state ordering agrees with experiment except for the $c 1Σu−$ state. Possible reasons for this discrepancy are discussed. The remaining errors in the bound‐state energy separations are rationalized. Data possibly bearing on the unobserved bound states are cited. Repulsive‐state curves are used to discuss predissociation in the Schumann–Runge bands and to illustrate avoided‐crossing phenomena.