The ground and first excited states of the I-3 radical are characterized by photoelectron spectroscopy of I-3(-) and Ar . I-3(-) at 266 nm. The electron affinity of I-3 is 4.226+/-0.013 eV. Based on the recently determined bond dissociation energy of I-3(-), the I-3 ground state is bound by 0.143+/-0.06 eV. The first excited state of I-3 lies 0.27 eV above the ground state. A vibrational progression is seen in the ground state band of the I-3(-) photoelectron spectrum. The addition of an argon atom to I-3(-) reduces the contribution of hot bands to the photoelectron spectrum, facilitating the interpretation of the vibrational structure. Simulations indicate that the I-3 ground state is linear with a symmetric stretch frequency of 115+/-5 cm(-1) and is likely to be centrosymmetric.