Peak and background structure of 3d photoemission spectra from fifth-period elements

We present a unified, state-of-the-art Coupled-Resonance (CR) and Narrow-Shirley (NS) framework for the comprehensive analysis of 3 d core-level photoemission spectra (XPS) of the fifth-row elements (Rb–Te). This novel methodology successfully overcomes the inherent challenges of these spectra, including pronounced main-peak asymmetry and complex, structured backgrounds, to deliver physically meaningful insights. By modeling interference among accessible final-state configurations, CR Type II and Type III lineshapes accurately reproduce asymmetric peak profiles, capturing both the sharp low-binding-energy onsets and gradual high-binding-energy decay. This systematic analysis reveals periodic trends in resonance energies, lifetime widths, and complex intensities that can be compared with first-principles calculations. Concurrently, the NS method resolves the intrinsic background, which is commonly approximated as a monotonic step, to reveal distinct, structured features. These intrinsic background peaks display a novel qualitative correspondence with features in K- and L 3 -edge Near-Edge X-ray Absorption Fine Structure (NEXAFS). This correlation supports the Interchannel-Coupling with Valence Band Losses (ICVBL) mechanism, involving valence electron excitation into specific unoccupied states. By rigorously isolating extrinsic scattering via Tougaard backgrounds, we ensure a robust distinction between intrinsic excitations and inelastic scattering. In summary, the CR–NS framework is a transferable methodology for resolving complex core-level lineshapes and intrinsic background structure. Although demonstrated here for pure metallic systems, the underlying analytical workflow provides a physically constrained basis for future analysis of more complex compounds and alloys, where separating intrinsic, extrinsic, and chemical-state contributions is essential for reliable electronic-structure interpretation.