  Slow magnetooscilations of the conductivity are observed in a 75 nm wide
quantum well at heating of the two-dimensional electrons by a high-intensity
surface acoustic wave. These magnetooscillations are caused by intersubband
elastic scattering between the symmetric and asymmetric subbands formed due to
an electrostatic barrier in the center of the quantum well. The tunneling
splitting between these subbands as well as the intersubband scattering rate
are determined.
