Rotational Analysis of the Absorption Spectrum of Heavy Oxygen (18O2) in the Region 1200–1285 Å

Abstract

The absorption spectrum of 18O2 has been photographed with a 6.65 m normal incidence type vacuum spectrograph in the 1070–1300 Å region. Rotational structures of the following bands have been analyzed; 1–0, 2–0, 3–0, and 4–0 of α1Σu+ ← X3Σg−; 2–0and 3–0 of β3Σu+ ← X3Σg−; and a strong band at 1246 Å. The upper state of the 1246 Å band is determined to have 3Σu− symmetry, and the transition is designated E3Σu− ← X3Σg−. These three upper states are Rydberg in character, with electron configuration (πu2p)4(πg2p)(3pπ). The observed rotational constants of the α1Σu+ and β3Σu+ states are nearly identical to those of the X2Πg state of O2+ to which these three Rydberg states converge. However, the rotational constant of the E3Σu− state, B1 = 1.3702 cm−1, is much smaller than the value B1 = 1.4764 cm−1 for the X2Πg state of 18O2+ estimated from the corresponding 16O2+ value. A brief discussion of this discrepancy is given.