Table 3 Calculated absorption peaks of L-hydroxyproline and vibration model analysis

1

0.76 THz

The vibration of the propyl alcohol group of the right pyrrolidine ring. Under the intermolecular hydrogen bond, the left molecule vibrates back and forth following the right molecule (see Fig. 1d).

2

1.17 THz

The torsion and vibration of the right pyrrolidine ring. Under the intermolecular hydrogen bond, the up-and-down vibration of the left L-hydroxyproline molecule causes the absorption peak at 1.17 THz (see Fig. 1e).

3

1.64 THz

The combination of the right-left vibration of the right molecule and the strong contractions of the left molecule (see Fig. 1f).