  We compare the theoretical predictions of the previous article [L. Benfatto
and M. B. Silva Neto, cond-mat/0602419], with Raman spectroscopy experiments in
Sr(2)CuO(2)Cl(2) and untwinned La(2)CuO(4) single crystals. We construct the
magnetic point group for the magnetically ordered phase of the two compounds,
Sr(2)CuO(2)Cl(2) and La(2)CuO(4), and we classify all the Raman active
one-magnon excitations according to the irreducible co-representations for the
associated magnetic point group. We then measure the evolution of the
one-magnon Raman energies and intensities for low and moderate magnetic fields
along the three crystallographic directions. In the case of La(2)CuO(4), we
demonstrate that from the jump of the Dzyaloshinskii-Moriya gap at the critical
magnetic field H_c ~ 6.6 T for the weak-ferromagnetic transition one can
determine the value of the interlayer coupling J_\perp/J ~ 3.2 x 10^-5. We
furthermore determine the components of the anisotropic gyromagnetic tensor as
g_s^a=2.0, g_s^b=2.08, and the upper bound g_s^c=2.65. For the case of
Sr(2)CuO(2)Cl(2), we compare the Raman data obtained in an in-plane magnetic
field with previous magnon-gap measurements done by ESR. Using the very low
magnon gap estimated by ESR (~ 0.05 meV), the data for the one-magnon Raman
energies agree reasonably well with the theoretical predictions for the case of
a transverse field (only hardening of the gap).
