  Tungsten is an important and versatile transition metal and has a firm place
at the heart of many technologies. A popular experimental technique for the
characterisation of tungsten and tungsten-based compounds is X-ray
photoelectron spectroscopy (XPS), which enables the assessment of chemical
states and electronic structure through the collection of core level and
valence band spectra. However, in the case of metallic tungsten, open questions
remain regarding the origin, nature, and position of satellite features that
are prominent in the photoelectron spectrum. These satellites are a fingerprint
of the electronic structure of the material and have not been thoroughly
investigated, at times leading to their misinterpretation. The present work
combines high-resolution soft and hard X-ray photoelectron spectroscopy (SXPS
and HAXPES) with reflection electron energy loss spectroscopy (REELS) and a
multi-tiered ab-initio theoretical approach, including density functional
theory (DFT) and many-body perturbation theory (G0W0 and GW+C), to disentangle
the complex set of experimentally observed satellite features attributed to the
generation of plasmons and interband transitions. This combined
experiment-theory strategy is able to uncover previously undocumented satellite
features, improving our understanding of their direct relationship to
tungsten's electronic structure. Furthermore, it lays the groundwork for future
studies into tungsten based mixed-metal systems and holds promise for the
re-assessment of the photoelectron spectra of other transition and
post-transition metals, where similar questions regarding satellite features
remain.
