A new magneto-optical effect in Raman spectroscopy

It is well known that the application of a static magnetic field can result in a change in both Raman spectral intensities and line positions. this effect is generally associated with a removal of spin degeneracy, and leads to a manifestation of chiral discrimination in both optically active and inactive samples. However, other magnetic field effects can be conferred upon the Raman process by virtue of direct magneto-optical interactions. It is here shown that for molecules belonging to one of the cubic or icosahedral point groups, any polarised Raman transition associated with a totally symmetric vibration becomes depolarised on application of a magnetic field directed along the usual right-angled direction of observation. Hence with a suitable polarisation filter, the corresponding Raman line can be “switched” into the spectrum by application of the field.