Far-Infrared Vibrational Spectra of L-Ascorbic Acid Investigated by Terahertz Time Domain Spectroscopy

The low frequency vibrational modes, index of refraction, and absorption of L-ascorbic acid from 0.2 to 2.4 THz have been studied by terahertz time domain spectroscopy at room temperature. It is found that there are four dominated vibrational modes at 1.80, 2.05, 2.21 and 2.34 THz and the refractive index, varying between 1.77 and 1.83, has a mean value 1.79 in the 0.2-2.4 THz range. In parallel with the experimental study, density functional theory is employed to simulate structure and vibrational frequencies of L-ascorbic acid. Based on the calculated results, the observed vibrational modes in the far infrared region are assigned.