The infrared spectra of the (HF)2, (DF)2 and HF-DF isotopomers have been investigated in neon matrices between 8000 and 20 cm−1. They significantly increase the number of one and two quanta vibrational transitions identified in matrices, especially those involving deuterated species, and also include relative intensity measurements. A straightforward assignment is proposed for five fundamental transitions of each isotopomer: the two H(D)F stretches (ν1, ν2) and three out of four intermolecular modes (ν4, ν5, ν6). The non-observation of the ν3 band, predicted by the calculations at high frequency and with a strong intensity, is unexplained. Two kinds of two quanta transitions have been identified: νintra + νinter, with νintra = ν1 or ν2 and νinter = ν4, ν5, ν6 and those involving only νintra
(2ν1, 2ν2 and ν1 + ν2). From the first set, one deduces the νinter frequencies in the first excited states of ν1
(free HF) and ν2
(H-bonded HF): they noticeably increase in the ν2 excited state, which corresponds to a strengthening of the hydrogen bond, but do not significantly vary in the ν1 excited state. Assuming the transferability of the anharmonicity coefficients xij = νi+j − (νi + νj), with i = 1, 2 and j = 4, 5, 6, from the neon matrix to the gas, we propose a new determination of the νinter frequencies in the gas phase which cannot be measured directly in the absence of molecular beam experiments in the far infrared. Finally, from the second set, the intramolecular anharmonicity coefficients x11, x22 and x12 are obtained for (HF)2.