New vibrational assignments for the autoionization bands of O2 based on isotope shifts

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Abstract
The relative photoionization efficiency curves of 16O2, 16O18O, and 18O2 have been obtained in the 660–1035 Å region. Based on the detailed analysis of the observed isotope shifts, the autoionizing peaks in the 855–1010 Å region were newly assigned. The strong peaks in the 900–1010 Å region, which had been classified as belonging to four different (H, H′, M, and M′) progressions, were assigned to a single progression of the 3sσg Rydberg state (H 3Πu) converging to O+2(a 4Πu). Similarly, the peaks in the 855–925 Å region were assigned to a single progression of the 3sσg Rydberg state (J 3Πu) converging to O+2(A 2Πu) . Molecular constants of these two states have been determined as follows, all in the unit of cm−1 except δ and re: H 3Πu; 3sσg, J 3Πu; 3sσg, D0=28 249±26, D0=21 832±33, ωe=1058.5±3.0, ωe=1 010.0±5.5, ωexe=10.56±0.20, ωexe=3.70±0.39, T0=99 639±10, T0=106 053±17, δ=1.096±0.001, δ=1.133±0.002. re=1.37±0.01 Å.