  We have analyzed data on the free ion yield observed in liquid isooctane
irradiated by Co60 gamma rays within the framework of the Onsager theory about
initial recombination. Several distribution functions describing the electron
thermalization distance have been used and compared with the experimental
results: a delta function, a Gaussian type function and an exponential
function.
  A linear dependence between free ion yield and external electric field has
been found at low electric field values (E<1.2 MV/m) in excellent agreement
with the Onsager theory. At higher electric field values we obtain a solution
in power series of the external field using the Onsager theory.
