Two-dimensional photoelectron spectroscopy of hydrogen iodide (HI) has been performed in the photon energy region of 11.10-14.85 eV, in order to investigate dynamical properties on autoionization and neutral dissociation of Rydberg states HI*(R-A) converging to HI+((A) over tilde (2)Sigma(1/2)(+)). A two-dimensional photoelectron spectrum exhibits strong vibrational excitation of HI+((X) over tilde (2)Pi) over a photon energy region from similar to12 to 13.7 eV, which is attributable to the autoionizing feature of the 5dpi HI*(R-A) state. A noticeable set of stripes in the photon energy region of 13.5-14.5 eV is assigned as resulting from autoionization of the atomic Rydberg states of I* converging to I+ (P-3(0) or P-3(1)). The formation of I* is understood in terms of predissociation of multiple HI*(R-A) states by way of the repulsive Rydberg potential curves converging to HI+((4)Pi(1/2)). (C) 2004 American Institute of Physics.