600—Å Band of Helium

Using the third-order spectrum of a 3-m grazing incidence-type vacuum spectrograph, the 600-Å band of helium was studied in combination with an uncondensed discharge of helium operated at liquid-nitrogen temperature as well as at room temperature. The 600-Å band is tentatively explained as originating in the transition, A 1Σu+—X 1Σg+ of He2, where the A state has a potential maximum and the molecule is formed at high vibration levels of the A state by a collision of two atoms, one normal (1s2 1S0) and one metastable state (1s2s 1S0), through the potential barrier. The observed intensity enhancement of the neon line at 600.04 Å is also discussed with relation to the 600-Å band.