Physical conditions derived from OII recombination lines in planetary
  nebulae and their implications
  Based on high quality observations of multiplet V1 of OII and the NLTE atomic
computations for OII we study the density and temperature of a sample of PNe.
We find that, in general, the densities derived from recombination lines of OII
are similar than the densities derived from forbidden lines. This implies that
the signature for oxygen rich clumps of high density and low temperature is
absent in most of the objects of our sample. Electron pressures derived from
the hotter zones are similar or slightly larger than those derived from the
colder zones, suggesting the presence of shock waves. The average temperatures
and t2 values derived from H, He and O lines are similar and consistent with
chemical homogeneity. These results suggest that the abundances of these
objects are the ones derived from recombination lines.
