  We report the observation of novel magnetoresistance oscillations induced by
the resonant inter-subband absorption in nondegenerate 2D electrons bound to
the surface of liquid helium. The oscillations are periodic in 1/B and
originate from the scattering-mediated transitions of the excited electrons
into the Landau states of the first subband. The structure of the oscillations
is affected by the collision broadening of the Landau levels and by
many-electron effects.
