The (X) over tilde (2) Sigma(u)(+) state of the I-2(-) anion has been fit to a Morse potential using data from two techniques: conventional and femtosecond photoelectron spectroscopy (FPES). Conventional photoelectron spectroscopy is used to determine the adiabatic electron affinity of I-2 as well as the well depth and equilibrium nuclear geometry of I-2(-). In the FPES experiment, the pump pulse induces coherent nuclear motion on the ground state of I-2(-) by resonant impulsive stimulated Raman scattering (RISRS), and the vibrational frequency of the anion is determined from the resulting oscillatory structure in the time-dependent photoelectron spectra. We find the electron affinity (EA) of I-2 to be 2.524 +/- 0.005 eV, the well depth (D-e) for I-2(-) to be 1.014 +/- 0.005 eV, the equilibrium internuclear separation (R-e) to be 3.205 +/- 0.005 Angstrom, and the vibrational frequency to be 110 +/- 2 cm(-1). These values for the I-2(-) potential parameters differ significantly from previous results. (C) 1997 American Institute of Physics.