  In this article, we study the charmed baryon states $\Lambda_c(2625)$ and
$\Xi_c(2815)$ with the spin-parity ${3\over 2}^-$ by subtracting the
contributions from the corresponding charmed baryon states with the spin-parity
${3\over 2}^+$ using the QCD sum rules, and suggest a formula $
\mu=\sqrt{M_{\Lambda_c/\Xi_c}^2-{\mathbb{M}}_c^2}$ with the effective mass
${\mathbb{M}}_c=1.8\,\rm{GeV}$ to determine the energy scales of the QCD
spectral densities, and make reasonable predictions for the masses and pole
residues. The numerical results indicate that the $\Lambda_c(2625)$ and
$\Xi_c(2815)$ have at least two remarkable under-structures.
