This question is in relation to the [FeCl4]- molecule, which is tetrahedral. I previously deduced, using symmetry analysis, that the vectors corresponding to the bonds of the molecule will be A1+T2, which, according to the table below and my scarce knowledge of spectroscopy, should mean that we will observe 1 IR band and 2 Raman bands. More specifically, we should see 3 IR stretching modes and 4 Raman stretching modes where 3 of the Raman ones will coincide with 3 IR ones and 1 will be Raman-unique (see character table at the bottom of the question).
This is a question from an assignment, which confirms my prediction with the data below and asks to sketch the stretching modes associated with each band. This is where I am stuck - I am yet to find a proper procedure to do this as most textbooks simply give the shapes of the modes with no explanation. I know that an IR stretch should involve a change in dipole moment, which rules out the 'breathing' mode, but this still leaves me guessing as to which ones will be correct as there are only 3 IR modes, but there are surely more ways than that to change the dipole moment?
