One-color two-photon ionization of methyl iodide, resulting in the CH3I+ and CD3I+ ions in the (X) over tilde (2)E(3/2) and (2)E(1/2) electronic states, is investigated using the zero kinetic energy (ZEKE) photoelectron technique. Unlike the conventional photoelectron spectra, the two-photon spectra are resonantly enhanced via the dissociative (A) over tilde-state continuum and exhibit an extensive vibrational structure. A long progression in the C-I stretching vibration nu 3(+) is observed, and reliable values for all the vibrational frequencies of the ions and for the ionization potentials are obtained. The appearance of the spectra is discussed in terms of consecutive two-photon absorption via a dissociative intermediate state and a time-dependent picture of spectroscopy. Experimental evidence for the influence of the asymmetric nu(6) vibration on the photodissociation process is presented. It is shown that two-photon ZEKE spectroscopy via a dissociative intermediate state can serve as a powerful probe of the photodissociation dynamics. It also allows one to explore regions of the ground-state potential energy surface of the ion that are far from equilibrium.