The (1:1) clusters of I 2,4,5-tetrafluorobenzene (TFB) with CH3CN, CH3OCH3, and NH3 were studied both experimentally and computationally. Using fluorescence-detected infrared (FDIR) spectroscopy, the aromatic C-H... X (X = N, O) hydrogen bond formation in the clusters was directly evidenced by a low-frequency shift and intensity enhancement of the aromatic C-H stretching vibration in the TFB moiety. The molecular structures, stabilization energies, and vibrational frequencies of the clusters were computed at the MP2/6-31+G* level. The observed low-frequency shifts of the aromatic C-H stretch in the clusters correlate with the proton affinities of the acceptor molecules. (c) 2005 Elsevier B.V. All rights reserved.