SPECTROSCOPIC STUDY OF EXCESS ELECTRONS IN LIQUID-HELIUM

The IR absorption spectra of electron bubbles in helium have been measured directly over the wavelength interval 5-8.5 mum using semiconductor lasers installed inside the cryostat. The characteristics of the 1s-1p absorption line have been studied as a function of pressure (over the range 2-40 atm) and temperature (2-4 K). The observed changes in the position of the center of the absorption line with temperature and pressure can be described in a simple model by introducing the effective surface tension of the bubble boundary as an adjustable parameter. The experimental absorption line turns out to be much wider than predicted by the theory. Data on the position of the line agree well with photomobility experiments.