## 3 Results  
Line Attribution at Room Temperature and Estimate of the Initial Water Content of PYR\({}_{14}\)-DCA  
Figure 2 displays a comparison of the experimental absorption spectrum of PYR\({}_{14}\)-DCA and the calculated ones for the single ions PYR\({}_{14}\) and DCA. The lines centered around 664, 903 and 1307 cm\({}^{-1}\) are attributable to the anion vibrations. Around 2200 cm\({}^{-1}\) one would computationally expect a triply degenerate absorption band with a high intensity due to DCA. In the real ionic liquid, the triple degeneracy is removed and three strong absorption bands centered around 2130, 2190 and 2230 cm\({}^{-1}\) are detected, similarly to the case of other ILs containing dicyanamide [34; 35; 36; 37]. All the other absorption bands between 600 and 3200 cm\({}^{-1}\) can be attributed to the vibrations of the PYR\({}_{14}\) anion, in particular CH bending and stretching modes are visible in the regions 1350-1500 and 2800-3200 cm\({}^{-1}\), respectively. The comparison of the experimental vibration frequencies with those computed for anion and cation provides evidence that below 1200 cm\({}^{-1}\), one has to use a frequency scaling factor of 0.97 for DCA anion, while no scaling factor is needed for the PYR\({}_{14}\) cation.  
Figure 1: Basic structure of the PYR\({}_{14}\) cation and the DCA anion.  
Above 3200 cm\({}^{-1}\), one observes the typical absorption bands of water. Despite the storage of sample in an inert atmosphere, during the charging of the cell, it absorbed a significant amount of water from the atmosphere. One can roughly estimate the concentration of H\({}_{2}\)O absorbed from air comparing the area of the water absorption bands of the two sample: PYR\({}_{14}\)-DCA and PYR\({}_{14}\)-DCA + H\({}_{2}\)O. The latter was obtained by adding 57 wt% of water to the former. Figure 3 reports a comparison of the spectra of the two samples in the region of the OH stretching bands.  
Figure 2: Comparison of the infrared absorbance of PYR\({}_{14}\)-DCA measured at 300 and 241 K on heating (upper part of the panels, the lines are vertically shifted for clarity) and the calculated absorbance for the isolated ions DCA and PYR\({}_{14}\) (lower part of the figures). For dicyanamide a scaling factor of the vibration frequencies of 0.97 was considered. The blue, magenta and yellow rectangles show the regions of the vibrations of the DCA anion, the PYR\({}_{14}\) cation and water, respectively. The scales of the vertical axes are the same in the three panels (as indicated in the left panel).  
The area of absorption bands is proportional to the concentration of the species giving rise to it. Calling \(c_{0}\) and \(c_{1}\) the water concentration absorbed from the atmosphere and the concentration of water added intentionally, \(A_{0}\) and \(A_{1}\) the area of the OH stretching bands in the as received and in the intentionally hydrated sample, one can write the following proportion--\(c_{0}\):\(A_{0}=c_{1}\):\(A_{1}\). Solved to calculate \(c_{0}\), one finally obtains \(c_{0}=c_{1}A_{0}/A_{1}\). In the present case \(A_{1}\)-\(2A_{0}\), and therefore, the concentration of water in PYR\({}_{14}\)-DCA is \(c_{0}\)-3.3 molecules of H\({}_{2}\)O per ionic couple, while the concentration of water in PYR\({}_{14}\)-DCA + H\({}_{2}\)O is \(c_{1}\)-6.6 molecules of H\({}_{2}\)O per ionic couple.  
It must be noted that the frequency of the bands due to OH stretching is a clear mark of the coordination of water molecules: in gases, where a very low coordination is expected, OH bands are visible above 3600 cm\({}^{-1}\)[9; 38]; bands between 3400 and 3500 cm\({}^{-1}\) are due to an intermediate coordination 2 or 3 of water molecules. Finally, the band centered around 3270 cm\({}^{-1}\) is typical of 4-fold coordination and was largely observed in pure water in the solid state [38].