Linked from
The 15 pages that link to Photoelectron spectroscopy, each with the reason it gives.
Electron configurationRelated: Its measured energy levels test and reveal electronic configurations.
Ionization energyRelated: It measures ionization energies and reveals electronic structure.
Aufbau principleRelated: Measured electron energies test and refine orbital-energy assignments.
Work functionRelated: Its energy measurements can determine a material’s surface work function.