  Various differential cross sections of high-energy photon splitting in the
electric fields of heavy atoms are calculated exactly in the parameter \al. The
consideration is based on the quasiclassical approach applicable for small
angles between all photon momenta. The expressions obtained are valid for
arbitrary transverse momenta of final photons . The detailed investigation of
the process is performed taking into account the effect of screening . The
exact cross section turns out to be noticeably smaller than the result obtained
in the Born approximation.
