Electron bubbles in a dense helium gas

Quantum molecular dynamics simulations show that electrons in a helium gas at 77 K and with densities 1.0 and 1.5 × 1022 cm-3 self-trap in bubbles that are stable on a time scale of picoseconds. When the density is reduced to 6 × 1021 cm-3, the electron does not self-trap but percolates through the gas. A signature of bubble formation is a strong peak in the optical absorption spectrum. The peak is due to intra-bobble dipole transitions and shifts to higher energy with increasing gas density. © 1990.