Abstract Distributions of vibrationally excited HF produced by Hg-photosensitized reactions of fluoroethylenes are determined by means of the IR emission measurement of HF fundamentals. The distributions are almost of Boltzmann type with temperatures of 11400, 13700, 7200, 5700, 5700, and 2200 K for respective parent molecules of CH2=CHF, CH3CF=CH2, CH2=CF2, cis-, trans-CHF=CHF, and CHF=CF2. The fractions of vibrational energy of HF† among the energies available for distribution in various degrees-of-freedom of product molecules are 19, 23, 11, 7.6, 7.6, and 1.7% for the above molecules, respectively. The statistical calculation results in much less energy disposal in HF vibration in the decompositions of CH2=CHF, CH3CF=CH2, and CH2=CF2, while the distributions of HFt in CHF=GHF and CHF=CF2 are closer to those predicted by the statistical calculation. The deactivation rate of HF† in CH2=CHF is about three times larger than that in CH2=CF2, and the latter values resemble those in HF.