Resonance Raman spectrum of the tetrabromoferrate(III) ion
Abstract
A resonance Raman spectrum has been obtained for the complex [(C2H5)4N][FeBr4] in the solid state. At least two progressions in the ν1(a1) fundamental have been observed, viz.nν1(to n= 7) and ν3+nν1(to n= 5) and/or ν4+nν1(to n= 6). The spectroscopic constants ω1and x11 have been determined to be 202.0 and –0.38 cm–1 respectively from an analysis of the nν1 progression. Excitation profiles have been measured for ν1 and ν3(Stokes and anti-Stokes) and for 2ν1(Stokes); these profiles demonstrate the different resonance conditions for Stokes and anti-Stokes Raman bands. A more detailed excitation profile has been measured for the ν1(Stokes) fundamental in the region of one of the ligand field transitions. This profile has a minimum at approximately ν00 and a maximum shifted by 250 ± 50 cm–1 towards lower wavenumbers, an observation which is attributed to interference effects. The ν1 fundamental has been found to exhibit unusual (so called “anomalous”) polarisation at resonance.