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 600 and 1100 Å. The spectrum is characterized by a very intense band of continuous emission peaking at approximately 800 Å, along with a series of less intense bands between the wavelengths of 600 and 710 Å. This continuum is interpreted in terms of the radiative dissociation of neutral helium molecules in the reaction $A{}_{}{}^1{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}\to X{}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$. The over-all intensity corresponds to about 5×${10}^{15}$ (photons/sec)/μA of 160-keV electron beam excitation. The uv fluorescence of electron-bombarded superfluid helium is by far the most intense emission of the excited liquid and may represent a useful source of uv light.