Oxides and oxohalides

Three oxides of xenon are known: xenon trioxide (XeO3) and xenon tetroxide (XeO4), both of which are dangerously explosive and powerful oxidizing agents. Xenon dioxide (XeO2) was reported in 2011 with a coordination number of four. XeO2 forms when xenon fluoride is poured over ice. Its crystal structure may allow it to replace silicon in silicate minerals. XeOO+ cation has been identified by infrared spectroscopy in solid argon.
Xenon does not react with oxygen directly; the trioxide is formed by the hydrolysis of XeF6:
XeF6 + 3 H2O → XeO3 + 6 HF
XeO3 is weakly acidic, dissolving in alkali to form unstable xenate salts containing the HXeO−
4 anion. These unstable salts easily disproportionate into xenon gas and perxenate salts, containing the XeO4−
6 anion.
Barium perxenate, when treated with concentrated sulfuric acid, yields gaseous xenon tetroxide:
Ba2XeO6 + 2 H2SO4 → 2 BaSO4 + 2 H2O + XeO4
To prevent decomposition, the xenon tetroxide thus formed is quickly cooled to form a pale-yellow solid. It explodes above −35.9 °C into xenon and oxygen gas.
A number of xenon oxyfluorides are known, including XeOF2, XeOF4, XeO2F2, and XeO3F2. XeOF2 is formed by the reaction of OF2 with xenon gas at low temperatures. It may also be obtained by the partial hydrolysis of XeF4. It disproportionates at −20 °C into XeF2 and XeO2F2.[92] XeOF4 is formed by the partial hydrolysis of XeF6,[93] or the reaction of XeF6 with sodium perxenate, Na4XeO6. The latter reaction also produces a small amount of XeO3F2. XeOF4 reacts with CsF to form the XeOF−
5 anion, while XeOF3 reacts with the alkali metal fluorides KF, RbF and CsF to form the XeOF−
4 anion.

Other compounds

Recently, there has been an interest in xenon compounds where xenon is directly bonded to a less electronegative element than fluorine or oxygen, particularly carbon. Electron-withdrawing groups, such as groups with fluorine substitution, are necessary to stabilize these compounds. Numerous such compounds have been characterized, including:[92][97]
C6F5–Xe+–N≡C–CH3, where C6F5 is the pentafluorophenyl group.
[C6F5]2Xe
C6F5–Xe–X, where X is CN, F, or Cl.
R–C≡C–Xe+, where R is C2F−
5 or tert-butyl.
C6F5–XeF+
2
(C6F5Xe)2Cl+
Other compounds containing xenon bonded to a less electronegative element include F–Xe–N(SO2F)2 and F–Xe–BF2. The latter is synthesized from dioxygenyl tetrafluoroborate, O2BF4, at −100 °C.
An unusual ion containing xenon is the tetraxenonogold(II) cation, AuXe2+
4, which contains Xe–Au bonds.[99] This ion occurs in the compound AuXe4(Sb2F11)2, and is remarkable in having direct chemical bonds between two notoriously unreactive atoms, xenon and gold, with xenon acting as a transition metal ligand.
In 1995, M. Räsänen and co-workers, scientists at the University of Helsinki in Finland, announced the preparation of xenon dihydride (HXeH), and later xenon hydride-hydroxide (HXeOH), hydroxenoacetylene (HXeCCH), and other Xe-containing molecules. In 2008, Khriachtchev et al. reported the preparation of HXeOXeH by the photolysis of water within a cryogenic xenon matrix. Deuterated molecules, HXeOD and DXeOH, have also been produced.

Clathrates and excimers

In addition to compounds where xenon forms a chemical bond, xenon can form clathrates—substances where xenon atoms are trapped by the crystalline lattice of another compound. An example is xenon hydrate (Xe·5.75 H2O), where xenon atoms occupy vacancies in a lattice of water molecules. This clathrate has a melting point of 24 °C. The deuterated version of this hydrate has also been produced. Such clathrate hydrates can occur naturally under conditions of high pressure, such as in Lake Vostok underneath the Antarctic ice sheet. Clathrate formation can be used to fractionally distill xenon, argon and krypton.
Xenon can also form endohedral fullerene compounds, where a xenon atom is trapped inside a fullerene molecule. The xenon atom trapped in the fullerene can be monitored via 129Xe nuclear magnetic resonance (NMR) spectroscopy. Using this technique, chemical reactions on the fullerene molecule can be analyzed, due to the sensitivity of the chemical shift of the xenon atom to its environment. However, the xenon atom also has an electronic influence on the reactivity of the fullerene.[108]
While xenon atoms are at their ground energy state, they repel each other and will not form a bond. When xenon atoms becomes energized, however, they can form an excimer (excited dimer) until the electrons return to the ground state. This entity is formed because the xenon atom tends to fill its outermost electronic shell, and can briefly do this by adding an electron from a neighboring xenon atom. The typical lifetime of a xenon excimer is 1–5 ns, and the decay releases photons with wavelengths of about 150 and 173 nm. Xenon can also form dimers with other elements, such as the halogens bromine, chlorine and fluorine.

Applications

Although xenon is rare and relatively expensive to extract from the Earth's atmosphere, it has a number of applications.

Illumination and optics Gas-discharge lamps

Xenon is used in light-emitting devices called xenon flash lamps, which are used in photographic flashes and stroboscopic lamps; to excite the active medium in lasers which then generate coherent light; and, occasionally, in bactericidal lamps. The first solid-state laser, invented in 1960, was pumped by a xenon flash lamp, and lasers used to power inertial confinement fusion are also pumped by xenon flash lamps.
Continuous, short-arc, high pressure xenon arc lamps have a color temperature closely approximating noon sunlight and are used in solar simulators. That is, the chromaticity of these lamps closely approximates a heated black body radiator that has a temperature close to that observed from the Sun. After they were first introduced during the 1940s, these lamps began replacing the shorter-lived carbon arc lamps in movie projectors. They are employed in typical 35mm and IMAX film projection systems, automotive HID headlights, high-end "tactical" flashlights and other specialized uses. These arc lamps are an excellent source of short wavelength ultraviolet radiation and they have intense emissions in the near infrared, which is used in some night vision systems.
The individual cells in a plasma display use a mixture of xenon and neon that is converted into a plasma using electrodes. The interaction of this plasma with the electrodes generates ultraviolet photons, which then excite the phosphor coating on the front of the display.
Xenon is used as a "starter gas" in high pressure sodium lamps. It has the lowest thermal conductivity and lowest ionization potential of all the non-radioactive noble gases. As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp. The low thermal conductivity minimizes thermal losses in the lamp while in the operating state, and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state, which allows the lamp to be more easily started. Xenon is the largest and heaviest non-radioactive noble gas and so its rate of diffusion and leakage through a glass or other envelope is minimal relative to alternative inert gases.

Lasers

In 1962, a group of researchers at Bell Laboratories discovered laser action in xenon, and later found that the laser gain was improved by adding helium to the lasing medium. The first excimer laser used a xenon dimer (Xe2) energized by a beam of electrons to produce stimulated emission at an ultraviolet wavelength of 176 nm. Xenon chloride and xenon fluoride have also been used in excimer (or, more accurately, exciplex) lasers. The xenon chloride excimer laser has been employed, for example, in certain dermatological uses.

Medical Anesthesia

Xenon has been used as a general anesthetic. Although it is expensive, anesthesia machines that can deliver xenon are about to appear on the European market, because advances in recovery and recycling of xenon have made it economically viable.
Two physiological mechanisms for xenon anesthesia have been proposed. The first one involves the inhibition of the calcium ATPase pump—the mechanism cells use to remove calcium (Ca2+)—in the cell membrane of synapses. This results from a conformational change when xenon binds to nonpolar sites inside the protein. The second mechanism focuses on the non-specific interactions between the anesthetic and the lipid membrane.
Xenon has a minimum alveolar concentration (MAC) of 72% at age 40, making it 44% more potent than N2O as an anesthetic. Thus it can be used in concentrations with oxygen that have a lower risk of hypoxia. Unlike nitrous oxide (N2O), xenon is not a greenhouse gas and so it is also viewed as environmentally friendly.[128] Xenon vented into the atmosphere is being returned to its original source, so no environmental impact is likely