The lowest energy rotamer of the E conformers has a CCOH dihedral of ca. 0 It has been detected in emission and absorption in a star forming region near the Galactic centre together with its parent formamide, HCONH 2 . The GUAPOS project indicated its presence, outside the Galactic centre, in the hot molecular cloud G31 and speculated that acetamide and more generally -C(O)NH -species are prevalent in massive and clustered star-forming regions akin to that in which our Sun was formed. The very low barrier to internal rotation of the methyl group of ca. 24 cm -1 means that syn, anti and perpendicular conformations have been found depending on the level of theory and basis set. Here the conformation is best declared as syn. The availability of multiple low-lying rotamers makes the rotational spectrum very complex and has also hindered computations of its thermochemistry such as entropy and heat capacity. An adiabatic ionisation energy of 9.71±0.02 eV has been determined by VUV photoionisation experiments using synchrotron and photoelectron/photoion coincidence spectroscopy, in excellent agreement with a G4 computed value 9.70 eV, Table .