Characterization of the I2− anion ground state using conventional and femtosecond photoelectron spectroscopy

The ${\mathrm{X̃\hspace{0.17em}}}^2{\Sigma }_u^{+}$ state of the ${\mathrm{I}}_{\mathrm{2}}^{\mathrm{-}}$ 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 ${\mathrm{I}}_{\mathrm{2}}$ as well as the well depth and equilibrium nuclear geometry of ${\mathrm{I}}_{\mathrm{2}}^{\mathrm{-}}.$ In the FPES experiment, the pump pulse induces coherent nuclear motion on the ground state of ${\mathrm{I}}_{\mathrm{2}}^{\mathrm{-}}$ 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 ${\mathrm{I}}_{\mathrm{2}}$ to be $\text{2.524±0.005\hspace{0.17em}}\mathrm{eV},$ the well depth ${\mathrm{(D}}_e)$ for ${\mathrm{I}}_{\mathrm{2}}^{\mathrm{-}}$ to be $\text{1.014±0.005\hspace{0.17em}}\mathrm{eV},$ the equilibrium internuclear separation ${\mathrm{(R}}_e)$ to be $\text{3.205±0.005\hspace{0.17em}Å,}$ and the vibrational frequency to be $\text{110±2\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}.$ These values for the ${\mathrm{I}}_{\mathrm{2}}^{\mathrm{-}}$ potential parameters differ significantly from previous results.