  We consider a semi-infinite spatially dispersive dielectric with unequal
transverse and longitudinal susceptibilities. The effect of the boundary is
characterized by arbitrary reflection coefficients for polarization waves in
the material that propagate to the surface. Specific values of these
coefficients correspond to various additional boundary conditions (ABC) for
Maxwell's equations. We derive the electromagnetic reflection and transmission
coefficients at the boundary and investigate their dependence on material
parameters and ABC. We also investigate the electromagnetic zero-point and
thermal spectral energy density outside the dielectric. The nonlocal response
removes the boundary divergence of the spectral energy density that is present
in a local model. The spectral energy density shows a large dependence on the
difference between the transverse and longitudinal susceptibilities, even at
distances up to 10nm from the boundary.
