  We have investigated the spectra of light-heavy quarkonia with the use of a
quantum-chromodynamic potential model which is similar to that used earlier for
the heavy quarkonia. An essential feature of our treatment is the inclusion of
the one-loop radiative corrections to the quark-antiquark potential, which
contribute significantly to the spin-splittings among the quarkonium energy
levels. Unlike $c\bar{c}$ and $b\bar{b}$, the potential for a light-heavy
system has a complicated dependence on the light and heavy quark masses $m$ and
$M$, and it contains a spin-orbit mixing term. We have obtained excellent
results for the observed energy levels of $D^0$, $D_s$, $B^0$, and $B_s$, and
we are able to provide predicted results for many unobserved energy levels. Our
potential parameters for different quarkonia satisfy the constraints of quantum
chromodynamics.
  We have also used our investigation to test the accuracy of the heavy quark
effective theory. We find that the heavy quark expansion yields generally good
results for the $B^0$ and $B_s$ energy levels provided that $M^{-1}$ and
$M^{-1}\ln M$ corrections are taken into account in the quark-antiquark
interactions. It does not, however, provide equally good results for the energy
levels of $D^0$ and $D_s$, which indicates that the effective theory can be
applied more accurately to the $b$ quark than the $c$ quark.
