Characterization of volatile organic compounds (VOCs) in their liquid-phase by terahertz time-domain spectroscopy

Abstract

In this work the terahertz spectra of benzene, toluene, p-xylene and styrene-four volatile organic compounds (VOCs) of interest in environmental pollution studies-have been measured in their liquid phase at room temperature using terahertz time-domain spectroscopy (THz-TDS). Their frequency-dependent refractive index and absorption coefficient have been extracted and analyzed in the spectral range from 0.2 to 2.5 THz. The optical properties of bi-component VOCs mixtures have also been investigated and described in terms of a linear combination of pure VOCs optical components.

Fig. 1.

a) Schematic optical layout of the experimental THz-TDS setup. b) Profiles of free space (blue dotted line) and empty sample cell (red solid line) THz signals are reported.

Fig. 2.

a) The refractive indexes and b) absorption coefficients of benzene, styrene, toluene and p-xylene vs. frequency. Arrows indicate not compensated water absorptions.

Fig. 3.

a) The refractive indexes and b) absorption coefficients of pure styrene (blue) and p-xylene (red) in their liquid phase at room temperature. The experimental data (green lines) of mixture can be well represented through a linear combination (purple lines) of optical data of pure styrene and p-xylene with volume fractions corresponding to their nominal values (see text).