Interconversions between oxalic acid monoamide rotamers: Photochemical process versus tunneling

► UV matrix irradiation converts (E,E)-oxalic acid amide (4) to its (E,Z)-rotamer 5. ► The back-reaction 4 → 5 seems to be governed by [H]tunneling. ► DFT computed IR spectra were used for the identification of 4 and 5.