In this letter we compare the terahertz time-domain and fourier-transform infrared spectra of tris and its mixtures with crown ether. We demonstrate the potential of all plasma-air based time-domain terahertz technique for the analysis of low-frequency vibrational spectra. The spectral features are interpreted using simulations of the crystalline structure and THz vibrational modes with the aid of the solid-state density functional theory. (C) 2012 Elsevier B.V. All rights reserved.