Measurements on dissociative ionization of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ by fast (16–25 MeV) protons are carried out in an effort to understand two-electron processes in collisional ionization. The high velocity limit of the ratio of cross sections, R, of two-electron processes to one-electron processes obtained from these measurements along with earlier data is used to obtain a universal scaling law for R as a function of projectile charge and energy, irrespective of the sign of the projectile charge. © 1996 The American Physical Society.

• Received 20 February 1996

DOI:https://doi.org/10.1103/PhysRevA.54.2925