USE OF RELATIVISTIC EFFECTIVE CORE POTENTIAL IN THE CALCULATION OF ELELCTRON-IMPACT TOTAL IONIZATION CROSS SECTIONS Winifred M. Huo* and Y.-K. Kim *NASA Ames Research Center, Moffett Field, CA 94035-1000 U.S.A. +National Institute of Standards and Technology, Gaithersburg, MD 20899-8423 U.S.A. Based on the Binary-Encounter-Bethe (BEB) model, the advantage of using relativistic effective core potentials (RECP) in the calculations of total ionization cross sections of heavy atoms or molecules containing heavy atoms is discussed. Numerical examples for Ar, Kr, Xe, and WF6 are presented.