Xenon is a noble gas with gas density 5.894 g/L and melting point −112 °C; present in air at only trace levels, it is extracted by cryogenic distillation of liquid air, yet its unique luminescence and ionization properties make it irreplaceable in several high-end fields. Illumination is its traditional use: high-pressure xenon lamps emit near-sunlight color at high correlated color temperature and excellent color rendering, so they dominate cinema projectors, automotive HID headlamps, operating-room lights and searchlights; xenon flash tubes power photographic fill, stroboscopic tachometry and laser pumping. In aerospace, xenon ion thrusters use xenon as propellant, ionizing it and accelerating the ions through high-voltage grids; with specific impulse far above chemical rockets and low but months-long thrust, they have become standard for station keeping on communications satellites and for deep-space probes. In medicine, xenon was studied as an inhaled anesthetic because it is potent, fast on and off, and minimally affects circulation. Liquid xenon, with its high density and high scintillation yield, is the target material for time-projection chambers in dark-matter direct-detection and neutrino experiments. Xenon also feeds excimer lasers and particle-physics detectors.
Xenon was long thought to be completely inert until the first noble-gas compound was synthesized in 1962. Xenon difluoride (XeF2), the most accessible and studied xenon compound, is a white crystal that hydrolyzes slowly in water; in semiconductor fabs it serves as a selective etchant for silicon and silicon dioxide, and as a fluorinating and oxidizing reagent. Xenon tetrafluoride (XeF4) and xenon hexafluoride (XeF6) are strong fluorinating agents; XeF6 is used in nuclear-fuel reprocessing to convert uranium into volatile uranium hexafluoride for gas-centrifuge isotope separation. Xenon trioxide (XeO3) is a powerful oxidizer and sensitive explosive that survives only briefly in aqueous solution and is used mainly in laboratory oxidation chemistry. Perxenates such as sodium perxenate (Na4XeO6) rank among the strongest solid oxidizers known. Excimers such as XeCl and XeF are the gain media of excimer lasers used in semiconductor lithography and ophthalmic surgery.
