Analysis of phase transitions in molecular solids: quantitative assessment of phonon-mode vs intra-molecular spectral data

The efficacy of phonon-mode spectral data (20–400 cm−1) in identifying and characterising phase transitions is for the first time compared directly with traditional "fingerprint" intra-molecular spectral data (400–3800 cm−1) for a model molecular system, using a range of statistical approaches and algorithms. Both data sets were collected in the same experiment, allowing a direct comparison. We find that phonon-mode data offer a reliable method of identifying phase transitions, whereas the intra-molecular are inherently unsuitable. Our results are likely to apply widely to solid-solid transformations.