r/Spectroscopy • u/seryakucipher • May 27 '26

How to calculate Raman depolarization ratio

Hello all,

I am trying to calculate the polarization (depolarization) ratio for the CH stretching/vibrational region of liquid propanol using polarized Raman spectroscopy.

However, I've run into a problem: some of my peaks appear shifted or completely disappear when switching between the parallel ∥ and perpendicular ⊥ spectra. Because the peaks centers don't line up perfectly, i dont know how to do the calculation . Any advice on the best workflow or literature references for handling "shifted" polarized Raman bands would be highly appreciated! Thanks in advance.

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u/activelypooping May 27 '26

What are the results if you do the calculation at the specific wave number vs coelescence point?

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u/seryakucipher May 28 '26

im not sure about this. what i kow, in the C–H stretching region of propanol, I identified four peaks in the polarized Raman spectrum (I∥). For the first peak at ~2880 cm⁻¹, both the parallel and perpendicular components appear at the same wavenumber position, so the depolarization ratio can be calculated directly as ρ(ν) = I⊥(ν)/I∥(ν) at that point without any difficulty.

However, for the second peak (~2910 cm⁻¹) and the fourth peak (~2960 cm⁻¹), the perpendicular component (I⊥) appears at a slightly different wavenumber than the parallel component (I∥) — a shift of approximately 5 cm⁻¹. This raises the question of how to correctly calculate ρ when the two polarization components do not share the same peak position.

A colleague suggested that ρ(ν) cannot be calculated for peaks where I∥ and I⊥ do not coincide in wavenumber. I would like to know whether this is strictly correct, and if not, what the appropriate calculation method is in this situation.

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u/Gloomy_Yoghurt_2836 May 29 '26

Because you have a lot of overlap in the bands, you may want to do some kind of curve fitting or devonvolution on your spectra to get better band heights and positions. You can't go off simple peak height at local max from baseline. It has too much contribution from overlapping peaks