In the absorption spectroscopy we can calculate transmittance $T$ of a given sample by comparing how the intensity of the incident beam $I_{0}$ is decreased with the distance (Lambert-Beer Law).
$A = -\ln{\frac{I}{I_{0}}}=\alpha L$
where $A$ is absorbence, $T = 1 -A$, $\alpha$ is an absorption coefficient and $L$ is the distance.
But I encountered something called Normalized transmittence I don't really understand how can I get it from measured data. Normalized how? It appears in scientific articles but I couldn't find any good source explaining it really.
I read that I should divide my measured $I$ by reference intensity (it can fluctuate so it is measured along the way too). So the normalized absorbance would be $A = -\ln{\frac{I}{I_{0}^2}}$ or just by definition $A = -\ln{\frac{I}{I_{0}}} $
Can anyone help me please?
The spectra then look like this:
[https://www.researchgate.net/figure/Hydrogen-cyanide-H-13-C-14-N-2-3-rotational-vibrational-band-spectrum-obtained-by_fig4_242279131]