  We investigate beta-interactions of free nucleons and their impact on the
electron fraction (Y_e) and r-process nucleosynthesis in ejecta characteristic
of binary neutron star mergers (BNSMs). For that we employ trajectories from a
relativistic BNSM model to represent the density-temperature evolutions in our
parametric study. In the high-density environment, positron captures decrease
the neutron richness at the high temperatures predicted by the hydrodynamic
simulation. Circumventing the complexities of modelling three-dimensional
neutrino transport, (anti)neutrino captures are parameterized in terms of
prescribed neutrino luminosities and mean energies, guided by published results
and assumed as constant in time. Depending sensitively on the adopted
neutrino-antineutrino luminosity ratio, neutrino processes increase Y_e to
values between 0.25 and 0.40, still allowing for a successful r-process
compatible with the observed solar abundance distribution and a significant
fraction of the ejecta consisting of r-process nuclei. If the electron neutrino
luminosities and mean energies are relatively large compared to the
antineutrino properties, the mean Y_e might reach values >0.40 so that neutrino
captures seriously compromise the success of the r-process. In this case, the
r-abundances remain compatible with the solar distribution, but the total
amount of ejected r-material is reduced to a few percent, because the
production of iron-peak elements is favored. Proper neutrino physics, in
particular also neutrino absorption, have to be included in BNSM simulations
before final conclusions can be drawn concerning r-processing in this
environment and concerning observational consequences like kilonovae, whose
peak brightness and color temperature are sensitive to the
composition-dependent opacity of the ejecta.
