Absorption Spectrum of the He2 Molecule in the 510–611-Å Range

New vacuum-uv absorption phenomena in helium are reported. The most important of these consist of bands between 600 and 611 Å. Individual bands exhibit diffuse rotational structure and together form a υ′ progression. They are attributed to the transition A 1Σu+←X 1Σg+ of He2. Several rotational constants Bυ for the upper state are noted. The dissociation energy and the term value of the upper state are estimated. A minimum height for the potential “hump” in the upper state is determined to be 0.059 eV. The close connection between the emission and absorption bands of He2 around 600 Å is indicated and discussed. The location of the He-continuum (emission) peak is worked out in relation to the A-state term value and the ground-state potential function. A number of absorption bands were also observed in the range from 510–600 Å. They are attributed to other singlet systems relating to ns and nd orbitals (n > 2).