Structure Factor Lineshape Model Gives Approximate Nanoscale Size Of Polar Aggregates In The Ionic Liquid N-Methyl-N-Propylpyrrolidinium Bis(Trifluoromethylsulfonyl)Imide

A Lorentzian lineshape model is developed and tested for the charge alternation peak in X-ray structure factors calculated from MD simulations for N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl) imide. Applying the model to published, experimental X-ray scattering data reproduces calculated cation-cation and anion-anion distances within 6% and implies that half of ionic aggregates are larger than 12.7 angstrom.