Femtosecond photoelectron spectroscopy of the I 2 2 anion : Characterization of the à 8 2 P g , 1 / 2 excited state

A potential energy curve for the Ã8 Pg ,1/2 state of I2 2 is constructed based on femtosecond photoelectron spectroscopy of the I2 2 Ã8 Pg ,1/2←X̃ Su1 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 Ã8 Pg ,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 Su 1 state of I2 2 @J. Chem. Phys. 107, 7613 ~1997!# yields a well depth (De) of 0.01760.010 eV for the Ã8 Pg ,1/2 state with an equilibrium bond length (Re) of 6.260.6 Å. These values differ significantly from previous semiempirical results. © 1999 American Institute of Physics. @S0021-9606~99!00207-X#