We demonstrate that the gauche conformation of 1H-nonafluorobutane contains a blue-shifting intramolecular hydrogen bond by recording its 5th overtone spectrum with cavity ringdown spectroscopy and performing electronic structure calculations. The magnitude of the blue-shift is enhanced in the overtone spectrum as compared to the fundamental. The energy difference between the gauche conformer and the lowest energy zigzag conformer is calculated to be 288 cm(-1) using density functional theory and determined to be 280 +/- 30 cm(-1) using temperature-dependent FTIR measurements. The -H... F- bonding interaction in the gauche conformer leads to changes in bond lengths as compared to the non-hydrogen bonded conformers. (c) 2005 Elsevier B.V. All rights reserved.