  We report on the first measurement of narrow photoassociation lines of
$^{40}$Ca near the ${^3P_1}+{^1S_0}$ asymptote related to the molecular states
$^3\Pi_u$ and $^3\Sigma^+_u$. The highly accurate binding energies and Zeeman
splittings are well described by a coupled channel theoretical model,
confirming theoretical predictions of long-range coefficients. Our analysis
shows that only the inclusion of both energies and Zeeman splittings provides
an accurate description of the long-range interaction potentials.
