Femtosecond photoelectron spectroscopy of the I2− anion: Characterization of the Ã′ 2Πg,1/2 excited state

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Abstract
A potential energy curve for the Ã′ 2Πg,1/2 state of I2− is constructed based on femtosecond photoelectron spectroscopy of the I2− Ã′ 2Πg,1/2←X̃ 2Σu+ transition at 780 nm. The experiment is sensitive to the slope of the repulsive potential wall, the well depth, equilibrium bond length, and the long-range attractive portion of the upper state potential. The Ã′ 2Πg,1/2 potential is fit to a piecewise potential which is flexible in each of these regions. Simulations of the spectrum using a previously determined Morse potential for the X̃ 2Σu+ state of I2− [J. Chem. Phys. 107, 7613 (1997)] yields a well depth (De) of 0.017±0.010 eV for the Ã′ 2Πg,1/2 state with an equilibrium bond length (Re) of 6.2±0.6 Å. These values differ significantly from previous semiempirical results.