Low-frequency collective vibrational modes of asparagine by terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy has been used to measure the spectral properties of polycrystalline asparagines at room temperature. The absorption spectra and the indexes of refraction are obtained. This result shows the sample has the spectral response in terahertz spectral range and the fact demonstrates the terahertz spectra of asparagine could be used to study the molecular structure and vibration of sample. Two absorption peaks, the broad band ranged from 1.642 to 1.758 THz and the narrow one located at 2.266 THz, are observed in the frequency range 0.5-2.4 THz. The assignments of vibrational modes in this spectral region are made using density functional theory at the level of B3LYP/6-31+G(d,p). The theoretical results agree well with the experimental data.