Is the Schumann-Runge continuum of oxygen structureless?

The absorption of supersonically expanded oxygen molecules was measured over the 1550-1380 Å range. The cold absorption spectrum shows resonances in the Schumann-Runge continuum, which have not been reported previously in room-temperature measurements. This spectrum was compared with the corresponding electron-loss spectrum as well as with the resonance-enhanced multi-photon ionization (REMPI) results. Although our cold bands do not coincide exactly with those of the electron- loss and REMPI spectra, they are assigned to the ³Π_g(3sσ_g) Rydberg state.