Resonance Raman and IR spectroscopic measurements of the two diazene-bridged systems [{Fe'NHS4'}(2-)(N2H2)] ('NHS4'(2-) = 2,2'-bis(2-mercaptophenylthio)diethylamine(2-)) (I) and [{Fe'S-4'(PPr3)}(2)(N2H2)] ('S-4'(2-) = 1,2-bis(2-mercaptophenylthio)ethane(2-)) (II) including H-2- and N-15-isotopomers are combined with a normal coordinate analysis (NCA) in order to describe the vibrational properties of diazene coordinated to Fe(II)-sulfur centers. Eight of the 12 normal modes of the Fe-N2H2-Fe unit have been identified by their isotope shifts. Most of the Raman-active diazene vibrations are resonance enhanced with respect to the 600 nm transition providing further support to the assignment of this band as Fe(d) to diazene(pi*) charge-transfer (MLCT) transition. The force constant for the N-N bond of 7.7 mdyn/Angstrom corresponds to a N-N bond order of about 1.5 and indicates that the diazene unit is moderately activated. The force constant of the Fe-N bond of 1.8 mdyn/Angstrom is about 2.5 times as large as for a simple sigma-bond. These values confirm the sigma-donor pi-acceptor formulation of the Fe-diazene bond presented in part 1 of this paper. The splitting of the diazene N-H and N-D vibrations observed in the Raman spectra of II is ascribed to a photoisomerization process taking place upon irradiation into the MLCT band.