Figure 2. Spectra of the (1-0) band of the 1Δg + 1Δg ← 3Σg-+3Σg-- a simultaneous path length tranSItion. of 122 m The and a upper slitwidth spectrum of about was 1.2 recorded cm-1. with The lower spectrum was recorded with a path length of 168 m and a slitwldth of about 2.5 cm-1. The oxygen density was 2.1 amagats at both temperatures. The tick mark indicates the band origin calculated from the spectroscopic constants of the free molecule.