Comment on ``Energy Dependence of Electron Lifetime in Graphite Observed   with Femtosecond Photoemission Spectroscopy'' (PRL 76, 483(1996).)
  We comment on the theoretical interpretations applied to a recent experiment on electron lifetime in graphite. We point out that the acoustic-plasmon excitations in a layered two-dimensional electron system do not produce a linear energy dependence for the Coulomb scattering rate. 
Lian Zheng and S. Das Sarma (Univ. of Maryland)