[X²Π_g]ndλ^1,3∧_g Rydberg states of O₂

Experimental observations of the gerade (g) states of O₂ that exist between the dissociation limit of the B³Σ_u^- state and the X²Π_g ground state of O₂⁺ are reexamined. Emphasis is placed on the assignment of electronic structures of the [X²Π_g]ndλ^1,3∧_g Rydberg states for which experimental data can be obtained from the literature: mainly, ndπ_g- and ndδ_g-based ^1,3∧_g states with n = 3-5 and the ndπ_g ¹Σ_g⁺ and ³_g^- series with n = 6-11. In many cases, characterizations of these electronic structures are limited by the quality of existing experimental data and, in cases where rotational band structures were analyzed, by the unavailability of most of the rotational energy level data upon which reported parameterizations were based. Thus, while a general picture of some segments of the ndπ_g - and ndδ_g-based structures can be presented, quantitative descriptions of these structures and unique identification of the causes of many apparent structural irregularities will not be possible until a new well-calibrated, rotationally resolved database is developed.