Raman spectra were processed using home-written MAT-LAB scripts. The spectra were first preprocessed by removing cosmic rays before being averaged. Spectra measured in the fingerprint region between 1100 -1600 cm -1 were calibrated using the 1266.3 and 1444.4 cm -1 bands of cyclohexane, while spectra measured in the low-frequency region (6 -500 cm -1 ) were calibrated against the 50.0, 153.8, 219.1, and 473.2 cm -1 bands of sulfur. Spectra were baselinecorrected with an asymmetrical least squares algorithm using a MATLAB application published by Felten et al.