  We theoretically calculate the finite wave vector plasmon dispersion in a low
density 2D electron layer taking into account finite temperature, finite layer
width, and local field corrections. We compare our theoretical results with
recent Raman scattering spectroscopic experimental 2D plasmon dispersion data
in GaAs quantum wells at very low carrier densities ($r_s > 10$) and large wave
vectors ($q \ge k_F$). We find good agreement with the experimental data,
providing an explanation for why the experimentally measured dispersion seems
to obey the simple classical long wavelength 2D plasmon dispersion formula. We
also provide a critical discussion on the observable manifestations of the
quantum-classical and the Wigner crystal - electron liquid crossover behavior
in the 2D plasmon properties as a function of electron density and temperature
in GaAs quantum well systems.
