  We present the Raman-scattering spectra of CaV2O5 and MgV2O5. The magnetic
contribution in the Raman spectra of CaV2O5 is found in the form of a strong
asymmetric line, centered at 2Delta, with a tail on the high-energy side. Our
analysis of its spectral shape shows that the magnetic ordering in CaV2O5 can
be described using a S=1/2 two-leg ladder Heisenberg antiferromagnetic model
with Jparallel/Jperp = 0.1, and a small interladder exchange. The spin gap and
exchange constant are estimated to be Delta = 400 cm-1 (570 K) and Jperp = 640
K. No magnon bound states are found. In contrast to CaV2O5 the existence of the
spin-gap is not confirmed in MgV2O5, since we found no feature in the spectra
which could be associated with the onset of the two-magnon continuum. Instead,
we observe two-magnon excitation at 340 cm-1, presumably related to the top of
the two-magnon brunch.
