  We present high resolution, long-slit spectra of the jet-cloud interaction in
the powerful southern radio galaxy PKS2250-41. We have resolved the emission
lines into two main kinematic components: a broad component (FWHM \geq 900
km/s) and a narrow component (FWHM \leq 150 km/s). While the broad component is
characterized by a low ionization level (with particular ly weak
HeII$\lambda$4686 emission) and is spatially associated with the radio lobe,
the narrow component is characterized by a higher ionization level and extends
well beyond the radio lobe. Crucially, we measure a higher electron temperature
for the broad component (T \sim 30,000 K) than for the narrow component (T \sim
15,000 K). The general line ratios and physical conditions of the two
components are consistent with a model in which the broad component r epresents
gas cooling behind the shock front driven by the radio jets, while the narrow
component represents the AGN- or shock-photoionized precursor gas. However,
uncertainties remain about the gas acceleration mechanism behind the shock
front: unless the radio components are expanding unusually fast in this source,
it is likely that entrainment of the warm clouds in the hot post-shock wind or
radio plasma is required.
  The similarities between the kinematic properties of PKS2250-41 and some high
redshift radio galaxies suggest that the ambient and the shocked gas have also
been resolved in the more distant objects. Given the evidence that the emission
line processes are affected by the interactions between the radio and the
optical structures, care must be taken when interpreting the UV spectra of high
redshift radio galaxies.
