  The inelastic lifetimes of electrons in image-potential states at Cu(100)
that are Stark-shifted by the electrostatic tip-sample interaction in the
scanning tunneling microscope are calculated using the many-body GW
approximation. The results demonstrate that in typical tunneling conditions the
image state lifetimes are significantly reduced from their field-free values.
The Stark-shift to higher energies increases the number of inelastic scattering
channels that are available for decay, with field-induced changes in the image
state wave function increasing the efficiency of the inelastic scattering
through greater overlap with final state wave functions.
