  The spin-orbit splittings in the spectra of nuclei with mass numbers 5, 15
and 17 are studied within the framework of shell-model configuration mixing
calculations including 2$\hbar \omega$ excitations. The contributions of the
two-body spin-orbit and tensor components of the nucleon-nucleon interaction
are studied in various model spaces. It is found that the effects of the
two-body spin-orbit interaction are dominant and quite sensitive to the size of
the model-space considered. The effects of the tensor interaction are weaker.
The correlations effects which are included in the larger (0+2) $\hbar \omega$
shell-model space reduce the spin-orbit splitting in the case of A=5 by 20%,
and enhance it for A=15 by about the same 20%. However, it is found that the
correlations have a very small effect on the $d_{3/2} - d_{5/2}$ splitting in
A=17.
