  VLT on-axis optical spectroscopy of the z=0.144 radio-loud quasar HE
1434-1600 is presented. The spatially resolved spectra of the host galaxy are
deconvolved and separated from those of the central quasar in order to study
the dynamics of the stars and gas as well as the physical conditions of the
ISM. We find that the host of HE 1434-1600 is an elliptical galaxy that resides
in a group of at least 5 member galaxies, and that most likely experienced a
recent collision with its nearest companion. Compared with other quasar host
galaxies, HE 1434-1600 has a highly ionized ISM. The ionization state
corresponds to that of typical Seyferts, but the ionized regions are not
distributed in a homogeneous way around the QSO, and are located preferentially
several kiloparsecs away from it. While the stellar absorption lines do not
show any significant velocity field, the gas emission lines do. The observed
gas velocity field is hard to reconcile with dynamical models involving
rotating disk, modified Hubble laws or power laws, that all require extreme
central masses (M > 10^9 M_sun) to provide only poor fit to the data. Power law
models, which best fit the data, provide a total mass of M(< 10 kpc)=9.2 10^10
M_sun. We conclude that the recent interaction between HE 1434-1600 and its
closest companion has strongly affected the gas velocity and ionization state,
from the center of the galaxy to its most external parts.
