Commercially available Terahertz (THz) Time domain spectroscopy (THz-TDS) apparatus are used in multiple application fields from material science to biology, and even in industry to measure the thickness of a paint layers. Its broad spectral coverage is of interest for air quality monitoring and atmospheric composition analysis. However, gas spectroscopy needs high resolution that the usual approach in THz-TDS is unable to provide. In this letter, we introduce the concept of constraint reconstruction for super-resolution spectroscopy based on the modeling of the spectroscopic rotational lines in a sparse spectrum. It is demonstrated for low-molecular weight molecules in gas phase that typically have spectra containing a small number of narrow lines over a broad spectrum. This alternative approach directly reconstructing the spectra achieved a resolution improvement factor of 10 compared to the best available resolution by the standard THz-TDS data treatment.