The intensity of HF (and DF) overtone emission from individual vibrational levels populated in the reactions: H + F2→ HF + F (1), F + H2→ HF + H(2)(and their deuterium analogues) has been studied as a function of the concentration of added quenching gases. Rate coefficients have been obtained for the transfer of energy from HF (2 ⩽v⩽ 7) to Q = CO, N2, O2, CO2, N2O, HCN, H2O, D2O, NH3, CH4 and SF6, and from DF (3 ⩽v⩽ 5) to Q = CO, N2, CO2, HCN and D2O. The results are discussed in relation to the influence of the rates of vibrational-to-vibrational (V-V) energy exchange of (a)Δν, the energy discrepancy between the vibrational transition energies, and (b) the infrared activity of the acceptor mode in Q. The role played by strong attractive forces in facilitating energy transfer is also considered.