  Structure and lattice dynamics of the (001) surface of Sr$_2$CuO$_2$Cl$_2$
have been studied by helium atom scattering (HAS). Analysis of diffraction
patterns obtained by elastic HAS revealed a surface periodicity consistent with
bulk termination, and confirms that the surface is non-polar and stable which
favors a SrCl surface termination. Bulk and surface lattice dynamical
calculations based on the shell-model were carried out to characterize the
experimental phonon dispersions obtained by inelastic HAS. No experimental
surface mode was observed above 200 cm$^{-1}$. Comparison between the
experimental data and theoretical results for two different slabs with SrCl and
CuO$_2$ terminations showed that the experimental data conforms exclusively
with the SrCl surface modes.
