The decay kinetics of highly mobile excess electrons formed on nanosecond pulse radiolysis of crystalline ice have been studied from -10 to -190/sup 0/C by using the microwave absorption method. The overall decay is controlled by four processes, two of which involve preexisting trapping sites present in the lattice and two others which involve reaction with products of irradiation formed in the pulse. The lattice trapping sites are tentatively assigned to a vacancy combined with a Bjerrum D defect (dressed vacancy) and a normal lattice vacancy. The former results in an electron decay rate (rate constant x trap concentration) of 1.1 x 10/sup 19/ exp(-0.48/kT) s/sup -1/, for kT in eV, above -80/sup 0/C and less than or equal to 10/sup 6/ s/sup -1/ below -100/sup 0/C. The latter is operative below -140/sup 0/C and presents a shallow trap, ..delta..H = -0.1 to -0.2 eV, for electrons. The main radiation product responsible for electron decay is the positive counterion. The electron-ion recombination rate constant is given by the Debye expression with a temperature-independent value of the effective dielectric constant epsilon/sub r/ of 2.1 +- 0.2. Based on an infinitely short pulse the first half-life of mobile electrons toward recombination ismore » approximately 500/R ns over the temperature range -120 to -50/sup 0/C, where R is the dose in the pulse in rads. The second product of irradiation which is thought to react with electrons is the OH radical with a rate constant of 3 x 10/sup 14//G(OH) dm/sup 3/ mol/sup -1/ (100 eV). The product of the electron mobility and the free-ion yield is found to increase from 3.0 x 10/sup -4/ to 4.2 x 10/sup -4/ m/sup 2/ V/sup -1/ s/sup -1/ (100 eV)-/sup 1/ over the temperature range -120 to -50/sup 0/C. Evidence for a second mobile species, thought to be the hole, with a mobility of ca. 1 x 10/sup -6/ m/sup 2/ V/sup -1/ s/sup -1/ and a lifetime of 50 to 100 ns is found above -40/sup 0/C.« less