Dynamics of the Formation of an Electron Bubble in Liquid Helium

The dynamics of excess electron localization in a bubble (equilibrium radius 17 {}) in liquid He is described in terms of the initial formation of an incipient bubble of radius 3.5{}, followed by an adiabatic bubble expansion in the ground electronic state, which is described by a hydrodynamic model for the expansion of a spherical cavity in an incompressible liquid. The bubble expansion time at pressure $P=0$ in liquid ⁴He is τb=3.9 ps; the expansion time exhibits a marked pressure dependence (e.g., τb=1.5 ps at $P=16$ atm) and a small (3%) isotope effect in liquid ³He. The interrogation of the electron bubble dynamics by femtosecond absorption spectroscopy is analyzed.