  The submillimeter-wave 3 cm{-1} < nu < 35 cm{-1} complex conductivity of the
reduced YBa2Cu3O{6+delta} film (Tc=56.5 K) was investigated for temperatures 4
K < T < 300 K and compared to the properties of the same film in the optimally
doped state. The frequency dependence of the effective quasiparticle scattering
rate 1/tau*(nu) was extracted from the spectra. 1/tau*(nu) is shown to be
frequency independent at low frequencies and high temperatures. A gradual
change to 1/tau*~nu^{1.5} law is observed as temperature decreases. In order to
explain the observed temperature dependence of the low frequency spectral
weight above Tc, the quasiparticle effective mass is supposed to be temperature
dependent for T>Tc.
