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 {}. The spectrum is characterized by a very intense band of continuous emission peaking at approximately 800 {}, along with a series of less intense bands between the wavelengths of 600 and 710 {}. This continuum is interpreted in terms of the radiative dissociation of neutral helium molecules in the reaction A¹Σᵤ⁺→X¹Σg⁺. The over-all intensity corresponds to about 5×{}10¹⁵ (photons/sec)/{μ}A 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.