The high-resolution Fourier transform infrared spectrum of trans-glyoxal in the gas phase has been recorded in the spectral regions 700–900 cm −1 , 1200–1400 cm −1 , and 1600–1800 cm −1 with a resolution ranging from 0.0020 to 0.0025 cm −1 . The spectrum displays extensive rotational structures which are assigned to the three fundamental bands ν 6 (A u , 801.5 cm −1 ), ν 10 (B u , 1732.1 cm −1 ), and ν 11 (B u , 1312.5 cm −1 ). A total of ca. 5000 absorption lines have been assigned to these three bands. A simultaneous ground state combination difference analysis of all three bands yields improved ground state spectroscopic constants for trans-glyoxal. Furthermore, a number of spectroscopic constants for the ν 6 and ν 11 levels have been determined for the first time.