  Recently observed splitting in angular resolved photoemission spectroscopy
(ARPES) on $\chem{Bi_2Sr_{2-x}La_xCuO_{6+\delta}}$ high--temperature
superconductor (Janowitz C. {\it et al.}, {\it Europhys. Lett.}, {\bf 60}
(2002) 615) is interpreted within the phenomenological Luttinger--liquid
framework, in which both the non--Fermi liquid scaling exponent of the spectral
function and the spin--charge separation are introduced. The anomalous Green
function with adjustable parameters fits very well to the Fermi edge and the
low--energy part of ARPES along the $\Gamma-M$ line in the Brillouin zone. In
contrast to one--dimensional models with Luttinger--liquid behavior we find
that both the anomalous scaling $\alpha$ and the parameter $\delta$ describing
the spin--charge separation are momentum dependent. The higher--energy part of
the spectra is not accounted for by this simple Luttinger--liquid form of the
Green function. In this energy regime additional scattering processes are
plausible to produce the experimentally observed wide incoherent background,
which diminishes as the inverse of the energy.
