Stick spectrum of mono-deuterated DME (symmetric conformer) in its vibrational ground state at 150 K (above) and 300 K (below). This figure illustrates the importance of the analysis around 1 THz. Although the dense ISM is generally colder, such temperatures exist in the warm inner regions of the collapsing protostars (see for instance Ceccarelli et al. 2000). The spectrum intensity scale is arbitrary.