  Electronic structure of ferromagnetic half-metal CrO$_2$ was studied by means
of 53Cr nuclear magnetic resonance (NMR) spectroscopy and density functional
theory (DFT). The measured NMR spectrum consists of three distinct spectral
lines and is interpreted as a triplet arising due to electric quadrupole
interaction. The observed NMR parameters agree well with those obtained from
electronic structure calculations, corresponding to the presence of Cr$^{4+}$
with fully occupied localized dxy singlet and partially occupied degenerated
dxz and dyz states, as required by ferromagnetic double exchange mechanism.
With high accuracy the orbital occupations and valence states of all Cr atoms
within the CrO$_2$ structure are found uniform.
