Concerning the appearance of the double peaks in the region 1450-1650 cm -1 of the IR spectrum of crystalline alanine in comparison to the single peaks structure of hydrated alanine, we report the corresponding effective modes in Fig. . In the figure, we selected two modes, one around 1450 cm -1 and one slightly above 1600 cm -1 . The modes on the left panels and on the right panels of Fig. are very similar: on the left, both modes involve the umbrella motion of NH 3 coupled to the (out-of-phase) umbrella motion in CH 3 ; on the right, both modes involve the HNH bending motion in NH 3 , coupled to an out-of-plane vibration of the third NH bond in the fragment. Therefore, it appears reasonable to assume that ω1=1044 cm -1 (h.) ω4=1134 cm -1 (h.)