  The recently discovered spin-active boron vacancy (V$_\text{B}^-$) defect
center in hexagonal boron nitride (hBN) has high contrast optically-detected
magnetic resonance (ODMR) at room-temperature, with a spin-triplet ground-state
that shows promise as a quantum sensor. Here we report temperature-dependent
ODMR spectroscopy to probe spin within the orbital excited-state. Our
experiments determine the excited-state spin Hamiltonian, including a
room-temperature zero-field splitting of 2.1 GHz and a g-factor similar to that
of the ground-state. We confirm that the resonance is associated with spin
rotation in the excited-state using pulsed ODMR measurements, and we observe
Zeeman-mediated level anti-crossings in both the orbital ground- and
excited-state. Our observation of a single set of excited-state spin-triplet
resonance from 10 to 300 K is consistent with an orbital-singlet, which has
consequences for understanding the symmetry of this defect. Additionally, the
excited-state ODMR has strong temperature dependence of both contrast and
transverse anisotropy splitting, enabling promising avenues for quantum
sensing.
