Glyoxal radical cations are produced in a pulsed discharge/supersonic molecular beam source. These ions are argon tagged and studied with mass-selected infrared laser photodissociation spectroscopy in the 1500-3500 cm(-1) region. Five vibrational resonances are detected, three of which are assigned to two CH stretches and the asymmetric CO stretch fundamentals. Additional bands are assigned to vibrational combinations based on anharmonic frequency calculations. DFT calculations of the internal rotation coordinate, and the comparison of the predicted versus experimental IR spectra, show that the radical cation has only one stable structure, the trans conformer. (C) 2015 Elsevier B.V. All rights reserved.