Ultraviolet Emission Spectrum of Electron-Bombarded Superfluid Helium

The emission spectrum of electron-bombarded superfluid helium has been measured as a function of wavelength between 550 and 2500 Å. The spectrum is characterized by a very intense asymmetric band of continuous emission peaking at approximately 800 Å with half-width of roughly 150 Å, along with a series of less intense bands between the wavelengths of 620 and 710 Å. This continuum is due to the radiative dissociation of neutral ${\mathrm{He}}_2$ molecules in the reaction $A{{}_{}{}^1{}_{}{}^{}\Sigma _u^{}{}_{}{}^{}}^{+}\to X{{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}}^{+}$.