Title: The Kinematics of the Permitted C II $λ$ 6578 Line in a Large Sample of Planetary Nebulae,
Abstract: We present spectroscopic observations of the C II $\lambda$6578 permitted
line for 83 lines of sight in 76 planetary nebulae at high spectral resolution,
most of them obtained with the Manchester Echelle Spectrograph on the 2.1\,m
telescope at the Observatorio Astronómico Nacional on the Sierra San Pedro
Mártir. We study the kinematics of the C II $\lambda$6578 permitted line with
respect to other permitted and collisionally-excited lines. Statistically, we
find that the kinematics of the C II $\lambda$6578 line are not those expected
if this line arises from the recombination of C$^{2+}$ ions or the fluorescence
of C$^+$ ions in ionization equilibrium in a chemically-homogeneous nebular
plasma, but instead its kinematics are those appropriate for a volume more
internal than expected. The planetary nebulae in this sample have well-defined
morphology and are restricted to a limited range in H$\alpha$ line widths (no
large values) compared to their counterparts in the Milky Way bulge, both of
which could be interpreted as the result of young nebular shells, an inference
that is also supported by nebular modeling. Concerning the long-standing
discrepancy between chemical abundances inferred from permitted and
collisionally-excited emission lines in photoionized nebulae, our results imply
that multiple plasma components occur commonly in planetary nebulae.