Experimental measurements coupled with Monte Carlo track simulations have been used to examine the yields of hydrated electrons in the radiolysis of water with protons, helium ions, and carbon ions. Glycylglycine, in concentrations ranging from 10(-4) to 1 M, was employed as a scavenger and the production of the ammonium cation used as a probe of hydrated electron yields from about 2 ns to 20 mus. Monte Carlo track simulations employing diffusion-kinetic calculations of product yields are found to reproduce experimental observations satisfactorily. Model details are used to elucidate the heavy ion track physics and chemistry. Comparison of the heavy ion results with those found in gamma radiolysis shows intratrack reactions are significant on the nanosecond to microsecond time scale as the ion track relaxes, and that a constant (escape) yield is never attained on this time scale. Numerical interpolation techniques are used to obtain both track average and track segment yields for use in practical applications or comparison with other models. The model results give the first hints that initial ( approximately 5 ps) hydrated electron yields, and possibly other water decomposition products, are dependent on the type and energy of the incident radiation.