Fully fluorinated non-carbon compounds NF₃ and SF₆ as ideal technosignature gases

Waste gas products from technological civilizations may accumulate in an exoplanet atmosphere to detectable levels. We propose nitrogen trifluoride (NF₃) and sulfur hexafluoride (SF₆) as ideal technosignature gases. Earth life avoids producing or using any N-F or S-F bond-containing molecules and makes no fully fluorinated molecules with any element. NF₃ and SF₆ may be universal technosignatures owing to their special industrial properties, which unlike biosignature gases, are not species-dependent. Other key relevant qualities of NF₃ and SF₆ are: their extremely low water solubility, unique spectral features, and long atmospheric lifetimes. NF₃ has no non-human sources and was absent from Earth's pre-industrial atmosphere. SF₆ is released in only tiny amounts from fluorine-containing minerals, and is likely produced in only trivial amounts by volcanic eruptions. We propose a strategy to rule out SF₆'s abiotic source by simultaneous observations of SiF₄, which is released by volcanoes in an order of magnitude higher abundance than SF₆. Other fully fluorinated human-made molecules are of interest, but their chemical and spectral properties are unavailable. We summarize why life on Earth-and perhaps life elsewhere-avoids using F. We caution, however, that we cannot definitively disentangle an alien biochemistry byproduct from a technosignature gas.