  The paper demonstrates possibility of giant enhancement of Surface Enhanced
Hyper Raman Scattering on the base of qualitative consideration of
electromagnetic field near some models of rough metal surfaces and of some
features of the dipole and quadrupole light-molecule interaction, such as it
was made in the dipole-quadrupole SERS theory. Consideration of symmetrical
molecules allows to obtain selection rules for their SEHR spectra and establish
such regularity as appearance of the lines, caused by totally symmetric
vibrations, transforming after the unit irreducible representation in molecules
with the groups, where the elements of symmetry change z on -z . These lines
are forbidden in usual HRS spectra. Analysis of literature data on phenazine
and pyrazine molecules demonstrates that their SEHR spectra can be explained by
the SEHRS dipole-quadrupole theory. Analysis of the SEHR spectra of these
molecules reveals appearance of strong forbidden bands, caused by vibrations
transforming after the unit irreducible representation that strongly confirms
this theory which allows to interpret the whole SEHR spectra in detail. The
results corroborate this common mechanism of Surface Enhanced optical processes
on molecules adsorbed on rough metal surfaces.
