  New elemental abundances for the neutron-capture elements Sr, Nb, Mo, Ru, La,
Sm, and Eu are presented for a large sample of 180 barium (Ba) giant stars, a
class of chemically peculiar objects that exhibit in their spectra enhancements
of the elements created by the $s$-process, as a consequence of mass transfer
between the components of a binary system. The content of heavy elements in
these stars, in fact, points to nucleosynthesis mechanisms that took place
within a former asymptotic giant branch (AGB) companion, now an invisible white
dwarf. From high-resolution ($R=48000$) spectra in the optical, we derived the
abundances either by equivalent width measurements or synthetic spectra
computations, and compared them with available data for field giant and dwarf
stars in the same range of metallicity. A re-determination of La abundances
resulted in [La/Fe] ratios up to 1.2 dex lower than values previously reported
in literature. The program Ba stars show overabundance of neutron-capture
elements, except for Eu, for which the observational data set behave similarly
to field stars. Comparison to model predictions are satisfactory for
second-to-first $s$-process peak ratios (e.g., [La/Sr]) and the ratios of the
predominantly $r$-process element Eu to La. However, the observed [Nb,Mo,Ru/Sr]
and [Ce,Nd,Sm/La] ratios show median values higher or at the upper limits of
the ranges of the model predictions. This unexplained feature calls for new
neutron capture models to be investigated.
