Charge and velocity dependence of the ratio of double to single ionizationof H- by Arq+ and Xeq+

Data and analysis for the ratio of double to single ionization of H- in col lisions with Arq+ and Xeq+ are presented for q = 1-6. Evidence is found for effects of electron screening in Ar+1 and Xe+1. The data are analyzed in t erms of both a Volkov-Keldysh approximation where the projectile field is s trong compared to the target and a Born expansion in the electron projectil e interaction where the projectile field is weak. At small q/v the H- data are consistent with the Born expansion while at lower energies a Volkov-Kel dysh calculation is in agreement with observation if in both analyses corre ction for electron screening is included. [S1050-2947(99)02006-5].