[en] In this work we present doubly-differential ionization cross section in fission fragments - N₂ collisions, in fission fragments - CO₂ collisions measured for electron ejection angles 30 deg, 45 deg, 60 deg and 90 deg and electron energy range from 10 eV to 1500 eV. Gas target is a gas jet and fission fragment source is ²⁵²Cf layer. Cross sections are measured in time-of-flight technique. The experimental results are compared with classical theory predictions. Comparison indicates on bad agreement with theory. We are calculated ionization energy loss by fission fragments in Cf-molecula collisions. The calculated ionization energy loss values based on experimental data are about 30-35% of full electronic energy loss for fission fragments in N₂ and CO₂ for the projectile energy ∼ 1 MeV/amu. 6 refs.; 4 figs