THEORETICAL AND EXPERIMENTAL INVESTIGATION OF TERAHERTZ ABSORPTION SPECTRA FOR WATER CLUSTERS [ IN THE ATMOSPHERE

The atmosphere transmission spectrum is measured from 0.2 to 1.6 THz with a continuous wave spectrometer. Three ring-formed water clusters of [([H.sub.2]O).sub.n] (n = 4, 5, 6) are proposed and their THz absorption spectra are calculated with the density functional theory. The calculated absorption lines of [([H.sub.2]O).sub.6] agree well with the measured spectrum, which indicates that the resonant absorptions in the atmosphere are caused by the ring-formed water clusters in the studied frequency range. The discrepancy between the calculation and experiment results on the absorptions around 1.2 THz should be ascribed to the deformation of the cluster.