Polarizability of Aspirin at Terahertz Frequencies Using Terahertz Time Domain Spectroscopy (THz-TDS)

作者：Zhang, Tianyao; Zhang, Zhaohui; Arnold, Mark A.^*

来源：Applied Spectroscopy, 2019, 73(3): 253-260.

DOI：10.1177/0003702818815177

• Terahertz time-domain spectroscopy
• THz-TDS
• THz spectroscopy
• polarizability measurements
• acetylsalicylic acid
• organic crystals
• effective medium model

A novel application of terahertz time-domain spectroscopy (THz-TDS) is described for the determination of permittivity and polarizability of organic crystals, as exemplified by measurements with the polymorph I form of crystalline aspirin (acetylsalicylic acid). The coherent nature of the THz pulse experiment, coupled with gated-detection, permits direct measure of differences in the phase angle of the electric field vector after passing through a pellet composed of the aspirin crystals embedded within an inert polymer matrix. An effective media model is used to extract dielectric information for the crystals from the measured time-domain signal that is representative of the entire pellet composition. Polarizability is then obtained for these organic crystals by using the Clausius-Mossotti relationship. Dielectric spectra and polarizability spectra are presented over the 0.3-3 THz frequency range (10-100 cm(-1)). The average polarizability values measured over the low frequency range (10-20 cm(-1)) are 22.4 +/- 0.3 and 22.4 +/- 0.5 angstrom(3) for aspirin crystals embedded within matrixes of polytetrafluoroethylene (PTFE) and polyethylene (PE), respectively.

• 单位
  北京科技大学