UVRR spectra were recorded using the multi-wavelengths UV Resonance Raman setup available at the BL10.2-IUVS beamline of Elettra Synchrotron Trieste (Italy). An excitation energy at 213 nm was set. All UVRR spectra were collected in back-scattered geometry by using a single pass of a Czerny-Turner spectrometer (Trivista 557, Princeton Instruments, 750 mm of focal length) equipped with a holographic grating at 1800g/mm and and with a Peltier-cooled CCD camera. The resolution was set at about 1.3 cm -1 /pixel. The spectrometer was calibrated with cyclohexane (spectroscopic grade, Merck). Any possible photo-damage was avoided by continuously spinning the sample cell during spectra acquisition. All samples were freshly prepared as described above and placed in quartz cuvettes for UVRR measurements. A sample holder equipped with a thermal bath coupled to a resistive heating system was used to control the temperature of the samples during the measurements (temperature stability of ±0.1 K). The temperature was set at 298 K unless otherwise indicated in the text.