High-resolution photoelectron spectroscopy

In molecular photoelectron spectroscopy (PES), electrons are ejected from molecules by irradiation of monochromatic photons with energy hn, (Formula Presented) The energy difference (DE) between a final ion state and an initial neutral state equals the incident photon energy minus the kinetic energy (KE) of the ejected electron, (Formula Presented) By defining adiabatic ionization energy (IE) as the minimum energy required to remove an electron from the ground electronic state of the neutral molecule, (Formula Presented) where E_i and E_n are the internal energies of the ionic and neutral states, which include excited electronic, vibrational, and rotational energies. If the initial neutral molecules are in their ground state, PES of neutral molecules provides information about the corresponding cations; if some of the neutral molecules are in their excited states, information about the neutral excited states may also be obtained. PES can also be used to study negative ions. In this case, the technique is termed as anion PES or photodetachment PES, (Formula Presented) where EA is the electron affinity of the anion that is the minimum energy required to eject an electron from the ground state of anion to the ground state of neutral molecule, and E_n and E_a are the internal energies of the neutral molecule and anion. About two decades ago, almost all valence photoelectron spectra of gas-phase metal complexes and clusters in the literature were broad without resolved vibrational energy levels.^1–5 Lack of vibrational structures impeded the direct investigation of metal-ligand bonding and molecular structures and....