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Thionyl chloride (SOCl$2$) is an extremely powerful oxidant widely used in industrial processes and playing a role in the chemistry of the atmosphere, \textit{J. Phys. Chem. A} 107, 6183 (2003)}. In addition, it has a molecular configuration similar to that of phosgene (COCl$2$), and is therefore of particular interest for security and defense applications. Low resolution vibrational spectra of gas phase SOCl$2$ 22,1193 (1954)} as well as high resolution pure rotational transitions up to 25 GHz 90, 3473 (1994)} have previously been investigated. To date no high resolution data are reported at frequencies higher than 25 GHz. \vspace{1em} We have investigated the THz absorption spectrum of SOCl$2$ in the spectral region 70--650 GHz using a frequency multiplier chain coupled to a 1 m long single path cell containing a pressure of about 15 $\mu$bar. At the time of the writing, about 8000 pure rotational transitions of SO$\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}$Cl$2$ with highest $J$ and $Ka$ values of 110 and 50 respectively have been assigned on the spectrum. We have also recorded the high resolution FIR spectra of SOCl$2$ in the spectral range 50--700 \wn~using synchrotron radiation at the AILES beamline of SOLEIL facility. A White-type cell aligned with an absorption path length of 150 m has been used to record, at a resolution of 0.001 \wn,~two spectra at pressures of 5 and 56 $\mu$bar of SOCl$2$. On these spectra all FIR modes of SOCl$2$ are observed ($\nu 2$ to $\nu 6$) and present a resolved rotational structure. Their analysis is in progress.