Ultraviolet Emission Spectrum of Electron-Bombarded Superfluid Helium

Abstract

The emission spectrum of electron-bombarded superfluid helium has been measured as a function of wavelength between 600 and 1100 \AA{}. The spectrum is characterized by a very intense band of continuous emission peaking at approximately 800 \AA{}, along with a series of less intense bands between the wavelengths of 600 and 710 \AA{}. This continuum is interpreted in terms of the radiative dissociation of neutral helium molecules in the reaction $A^{1}\ensuremath{\Sigma}_{u}^{+}\ensuremath{\rightarrow}X^{1}\ensuremath{\Sigma}_{g}^{+}$. The over-all intensity corresponds to about 5\ifmmode\times\else\texttimes\fi{}${10}^{15}$ (photons/sec)/\ensuremath{\mu}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.