The spectral characteristics of polycrystalline sulfur-containing amino acids L-methionine and L-cysteine in a THz range were studied by calculation and terahertz time-domain spectroscopy (THz-TDS) technologies. The absorption spectra and the indexes of refraction were obtained. The experimental results show that the sample has the spectral response in the terahertz spectral range and the terahertz spectra of sulfur-containing amino acids could be used to study the molecular structure and low-frequence collective vibrational modes. The absorption peaks in the frequency range of 0.2～2.8 THz have found at 1.06, 1.88 and 2.70 THz (for methionine), and 1.40, 1.70, 2.33 and 2.61 THz (for cysteine) by THz-TDS, respectively. The average refractive indexes are all 1.44. The vibration absorption spectra of bimolecular L-methionine have been calculated based on HF theory of Gaussian 03. The vibration rotation modes corresponding to the absorption peaks of L-methionine are presented.

Key words: terahertz time-domain spectroscopy, sulfur-containing amino acid, Hartree-Fock