Bandlike Structure from Continuum—Continuum Emission: The He2 600-Å Bands

The continuous spectrum produced by the radiative de-excitation of metastable atoms by atom impact is an example of molecular continuum—continuum transitions. It is shown that if the upper molecular state has a deep attractive well and the lower state is repulsive, the continuous spectrum will show bandlike structure similar to that obtained in bound—continuum transitions from high vibrational states. The analysis is applied to the radiative de-excitation of He(21S) by He, which gives rise to the ``600-Å bands.'' The structure and temperature dependence of these bands are well explained as bandlike continuum—continuum emission. Bandlike continua observed in other rare gases are briefly discussed in terms of the molecular states involved.