Soret-excitation resonance Raman (RR) spectra are reported for the bis-imidazole complexes of a series of mono- and divinylhemins. The complexes include 2-vinyldeuterohemin IX, 4-vinyldeuterohemin IX, protohemin IX, and protohemin III. For all four hemins, two polarized RR bands are observed at similar to 1620 and similar to 1631 cm(-1). Both of these bands are absent from the spectrum of the deuterohemin IX, which contains no vinyl substitutents, The relative intensities of the 1620- and 1631-cm(-1) bands are similar to 60:40 for all of the vinylhemins studied. However, the intensity of each band of both monovinyl complexes is approximately one-half that of the analogous bands of both divinyl complexes. The appearance of the 1620- and 1631-cm(-1) bands is independent of solvent although the 1631-cm(-1) band is difficult to identify in aqueous solutions wherein the hemins are aggregated. Temperature-dependent RR studies indicate that the intensity of the 1630-cm(-1) band monotonically decreases relative to that of the 1620-cm(-1) feature as the temperature is lowered. The 1620-cm(-1) feature has generally been assigned as the characteristic vinyl stretching mode (nu(C=C)) of vinylhemins. The 1631-cm(-1) band has not been previously identified in the RR spectra of vinylhemins in solution but has been observed in the spectra of heme proteins which d has been assigned as a second nu(C=C) mode. The appearance of two nu(C=C) modes has generally been attributed to site-specific vinyl group-protein interactions which render the 2- and 4-vinyl substituents of the protohemin IX cofactor inequivalent.