Spectra of the (0-0) band of the 1Δg + 1Δg ← 3Σg-+3Σg- simultaneous transition. The pathlength is 168 m. The slitwidth is 1 cm-1. The oxygen density is 2.1 amagats at temperature 87°K.
The collision‐induced absorption spectra have been measured at room temperature and at 87°K for bands in the 1Δg + 1Δg ← 3Σg− + 3Σg− and 1Δg + 1Σg+ ← 3Σg− + 3Σg− simultaneous electronic systems for oxygen. The binary absorption coefficients were found to increase with decreasing temperature for 1Δg + 1Δg ← 3Σg− + 3Σg−. The band shapes for this system suggest that the Hamiltonian which is responsible for intensity borrowing depends on the angular orientation of the O2 molecules in the collision pair since ΔK = 0,± 2,± 4 selection rules are needed to account for the Δν1 / 2 ∼ 200cm−1 bandwidth. The relative intensity of the (1–0) and (0–0) bands indicates that the interaction Hamiltonian is also strongly modulated by the vibrational coordinates of O2. The frequency shift of this simultaneous transition indicates that the intermolecular distance parameter for 1Δg⋅⋅⋅1Δg is 3% larger than for 3Σg−⋅⋅⋅3Σg−. The unusual band shape for the 1Δg + 1Σg+ ← 3Σg− + 3Σg− band is interpreted in terms of an exiton interaction for the 1Δg⋅⋅⋅1Σg>+ combination. Although bound state (O2)2 molecules undoubtedly exist at low temperatures these data provide no unambiguous spectroscopic evidence of their presence.
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