Infrared Spectrum of the Electron Bubble in Liquid Helium.

The energy of the ground state to first excited state electronic transition in the electron bubble in liquid helium has been measured at 1.3K and found to be 0.122 eV at a pressure of 1.1 atm and increasing to 0.209 eV at 18.3 atm. The position of a line in the P-T plane where the photoconductivity signal vanishes indicates that the signal arises from electron bubbles trapped on vorticity. The spherical square well model of the electron bubble accounts well for the transition energies if the effective surface tension is taken to be independent of pressure. This model also yields values for the electron bubble radius as a function of pressure that agree with the radius deduced by Ostermeier from mobility measurements.