The 123.6 nm photoionization of deuterated isooctane at -10 degrees C in the presence of hexafluorobenzene has been studied by examining the effect of a magnetic field to alter the quantum yield of recombination fluorescence. This fluorescence results from geminate recombination of hexafluorobenzene anions with isooctane positive ions. The use of a deuterated as contrasted to a protonated alkane makes the intensity of the recombination fluorescence much more sensitive to the magnetic field and permits observation of two maxima in the fluorescence yield at field strengths of 0 and 411 G and a possible third maximum at 822 G. The theory of the hyperfine induced spin evolution predicts these resonances at selected multiples of the C6F6- hyperfine constant of 137 G. Utilizing the diffusion theory of geminate recombination in a Coulomb field, the experimental magnetic field spectrum is found to be well predicted over most of the range of magnetic field strengths studied (up to 2.5 kG) by a simple, one parameter, exponential radial probability density of initial scavenged geminate pair separation distances.