  We use single-spin resonant spectroscopy to study the spin structure in the
orbital excited-state of a diamond nitrogen-vacancy center at room temperature.
We find that the excited state spin levels have a zero-field splitting that is
approximately half of the value of the ground state levels, a g-factor similar
to the ground state value, and a hyperfine splitting ~20x larger than in the
ground state. In addition, the width of the resonances reflects the electronic
lifetime in the excited state. We also show that the spin-splitting can
significantly differ between NV centers, likely due to the effects of local
strain, which provides a pathway to control over the spin Hamiltonian and may
be useful for quantum information processing.
