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

Abstract

The X̃ 2Σu+ state of the I2− 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 I2 as well as the well depth and equilibrium nuclear geometry of I2−. In the FPES experiment, the pump pulse induces coherent nuclear motion on the ground state of I2− 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 I2 to be 2.524±0.005 eV, the well depth (De) for I2− to be 1.014±0.005 eV, the equilibrium internuclear separation (Re) to be 3.205±0.005 Å, and the vibrational frequency to be 110±2 cm−1. These values for the I2− potential parameters differ significantly from previous results.