  We performed far-infrared and submillimeter-wave conductivity experiments in
the electron-doped cuprate La_{2-x}Ce_xCuO_4 with x = 0.081 (underdoped regime,
T_c = 25 K). The onset of the absorption in the superconducting state is
gradual in frequency and is inconsistent with the isotropic s-wave gap.
Instead, a narrow quasiparticle peak is observed at zero frequency and a second
peak at finite frequencies, clear fingerprints of the conductivity in a d-wave
superconductor. A far-infrared conductivity peak can be attributed to 4Delta_0,
or to 2Delta_0 + Delta_spin, where Delta_spin is the resonance frequency of the
spin-fluctuations. The infrared conductivity as well as the suppression of the
quasiparticle scattering rate below T_c are qualitatively similar to the
results in the hole-doped cuprates.
