Comparison of two spectra in order to find whether the irradiated sample has significantly different resulting spectra
Why don't you start with the simplest possible approach. I am sure there are very fancy spectral matching statistical algorithms, but simplicity has its own beauty. Comparing an inteferogram (not many features there) might be difficult but what about absorbance rather?
Look at the absorbance difference spectrum: (Spectrum after irradiation)-(Original sample spectrum). How does the plot look like? What is the signal which you are collecting? Sometimes the human eye can save a lot of time rather than doing significance testing on data points and forming null hypotheses.
The features which remain the same will be zero now and the features which change will be visible in the the difference spectrum.
Alternatively, you can take the first derivative of both spectra and smooth it with Savitsky-Golay or study the difference of &quot;first derivatives&quot;. Noise will be an issue but I guess you can take care of that.