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[en] Highlights: • TFAA exhibits similar gas-phase UV-initiated HF elimination to HFAA. • Collisional quenching reduces the relative quantum yield for TFAA and HFAA by 25×. • A strong collision model allows determination of photodissociation rate constants. • The TFAA rate constant is somewhat larger than that for HFAA. • Photoelimination appears to be the primary fate at sufficiently low pressure. The photochemistry of gas-phase 1,1,1-trifluoroacetylacetone (TFAA) and 1,1,1,5,5,5-hexafluoroacetylacetone (HFAA) excited with ultraviolet light involves a significant photoelimination channel producing HF and difluoromethylfuranone or pentafluoromethylfuranone, respectively. We report collisional self-quenching of the experimentally-determined relative quantum yield, and determine rate constants of 0.27 ± 0.03 and 0.33 ± 0.04 μs−1, for HFAA and TFAA respectively. A strong collision model is consistent with the observed quenching. The data suggest that this elimination is the primary photochemical fate at low pressure in both cases. The TFAA rate constant is larger than that for HFAA, in spite of TFAA having half as many fluorine atoms as HFAA.