Help needed! Raman spectrography: How to determine what elements are raman active given Wyckoff positions and group position

Hi!

I’m having a horrendous time trying to figure this out and it’s driving me crazy. An example question I was given was like so:

The Pyroxene group mineral diopside crystallizes in the monoclinic structure. The chemical formula, structural data, space group site positions, and list of all possible Raman modes are provided below. Find number and symmetry of Raman active modes for this mineral. Which elements in the chemical formula will contribute to vibrations represented as Raman active bands in the spectra

Chemical formula: MgCaSi2O6 Space group: C2/c (#15), Z = 4 (formula units in crystallographic unit cell) a = 9.7456 Å, b = 8.9198 Å, c = 5.2516 Å, α = γ = 90 deg, β = 105.86 deg

Atom X Y Z
Si 0.28627 0.09330 0.22936
Mg1 0 0.90814 0.25
Ca2 0 0.30144 0.25
O1 0.11550 0.08728 0.14220
O2 0.36136 0.25013 0.31830
O3 0.35083 0.01759 0.99530

Site positions for the space group C2/c

8f: x, y, z

4e: 0, y, 1/4

4d: 1/4, 1/4, 1/2

4c: 1/4, 1/4, 0

4b: 0, 1/2, 0

4a: 0, 0, 0

All Possible Raman modes for the space group C2/c:

WP:
8f: Ag = 3, Bg = 3
4e: Ag = 1, Bg = 2

Understanding how to do this is crucial because I have an exam coming up very soon that I know will ask something just like this and I am completely lost how, from this, I can tell which elements are “raman active” – please explain it to me like I know nothing about this – because I don’t – in the simplest way possible, if anyone can, you’d be my hero!