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.