Characterization of the I3 radical by anion photoelectron spectroscopy

The ground and first excited states of the I3 radical are characterized by photoelectron spectroscopy of I3− and Ar⋅I3− at 266 nm. The electron affinity of I3 is 4.226±0.013 eV. Based on the recently determined bond dissociation energy of I3−, the I3 ground state is bound by 0.143±0.06 eV. The first excited state of I3 lies 0.27 eV above the ground state. A vibrational progression is seen in the ground state band of the I3− photoelectron spectrum. The addition of an argon atom to I3− reduces the contribution of hot bands to the photoelectron spectrum, facilitating the interpretation of the vibrational structure. Simulations indicate that the I3 ground state is linear with a symmetric stretch frequency of 115±5 cm−1 and is likely to be centrosymmetric.