A Monte Carlo random flights technique is presented for simulating ion
-pair recombination kinetics in systems with diffusional and dielectri
c anisotropy, and is applied to geminate electron-hole recombination i
n anthracene and naphthalene. While the importance of the anisotropy i
s evident in the dependence of the escape probability on the orientati
on of the initial interion vector, it is found to be more significant
in determining the time-scale of the reaction kinetics, which can vary
by a factor of up to three in the systems studied. Comparisons for pa
irs with the same escape probability indicate that reaction in anthrac
ene is likely to be considerably faster than in naphthalene.