Synchrotron-based far-infrared spectra and analysis of the ν13, ν19 and ν20 bands of β-propiolactone

► Far-IR synchrotron light yields high quality rovibrational spectra. ► Three new vibrational states of β-propiolactone were investigated. ► Unambiguous assignment of carbonyl in-plane and out-of-plane vibrations. ► Band origins agree with ab initio calculations to within 10 cm-1.