  The delicate interplay of electronic charge, spin, and orbital degrees of
freedom is in the heart of many novel phenomena across the transition metal
oxide family. Here, by combining high- resolution angle resolved photoemission
spectroscopy and first principles calculations (with and without spin-orbit
coupling), the electronic structure of the rutile binary iridate, IrO$_2$ is
investigated. The detailed study of electronic bands measured on a high-quality
single crystalline sample, and use of a wide range of photon energy provide a
huge improvement over the previous studies. The excellent agreement between
theory and experimental results shows that the single-particle DFT description
of IrO$_2$ band structure is adequate, without the need of invoking any
treatment of correlation effects. Although many observed features point to a 3D
nature of the electronic structure, clear surface effects are revealed. The
discussion of the orbital character of the relevant bands crossing the Fermi
level sheds light on spin orbit coupling-driven phenomena in this material,
unveiling a spin-orbit induced avoided crossing, a property likely to play key
role in its large spin Hall effect.
