Additional conformer observed in the microwave spectrum of methyl vinyl ketone

► Two conformers were observed in the microwave spectrum of methyl vinyl ketone. ► Torsional barrier heights were calculated using the fitting programs JB95 and XIAM. ► Isotopologue rotational lines were assigned for ap- and sp-methyl vinyl ketone. ► Kraitchman analysis was completed for ap-and sp-methyl vinyl ketone heavy atoms.