The ν21 ring puckering mode of 3-oxetanone: A far infrared spectroscopic investigation using synchrotron radiation

► Ring puckering mode of 3-oxetanone and first three hotbands observed and assigned. ► Band centers fit to obtain ring puckering potential of form V = ax4 + bx2. ► Variation of rotational constants with vibrational state confirm that potential is fairly harmonic.