  Injection of photoelectrons into gaseous or liquid dielectrics is a widely
used technique to produce cold plasmas in weakly ionized systems for
investigating the transport properties of electrons. We report measurements of
the collection efficiency of photoelectrons injected into dense argon gas for
$T=152.7 $K, close to the critical temperature $T_{c}\approx 150.9 $K, and for
$T=200.0 $K. The high-field data agree with the Young-Bradbury model and with
previous measurements below $T_{c}$ and at an intermediate temperature above
$T_c .$ The effective, density-dependent electron-atom momentum transfer
scattering cross section can be deduced. However, the weak-field data near
$T_{c}$ show large deviations from the theoretical model. We show that the
electron behavior at weak field is influenced by electrostriction effects that
are only important near the critical point.
