# Chemicals/Argons

Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas.

## Emissions

Argon has three emission lines that occur in an electron cyclotron resonance (ECR) heated plasmas: 497.216, 500.9334, and 506.204 nm from Ar II.
Argon has an emission line occurring in the solar corona at 553.6 nm from Ar X.
Argon has an emission line that occurs in an electron cyclotron resonance (ECR) heated plasmas: 473.591 nm from Ar II.
Argon has several emission lines that occur in an electron cyclotron resonance (ECR) heated plasmas: 426.653, 428.29, 433.12, 434.8064, 437.075, 437.967, 442.60, and 443.019 nm from Ar II.

## Infrareds

The spectrum (center) was taken with a diffraction grating and a RasPi NoIR camera and an amber filter. Wavelengths from 605-680nm show up as red; 680-790nm as yellow; 790-1100nm as blue. The leftmost two bright "yellow" lines were visible with the eye as a deep red, of similar brightness to the next red line over to the left.

## Plasmas

Argon has several emission lines that occur in an electron cyclotron resonance (ECR) heated plasmas: 426.653, 428.29, 433.12, 434.8064, 437.075, 437.967, 442.60, and 443.019 nm from Ar II.

## Gases

Argon is a noble gas.

## Liquids

Liquid argon is used as the target for neutrino experiments and direct dark matter searches. The interaction between the hypothetical Weakly interacting massive particles (WIMPs) and an argon nucleus produces scintillation light that is detected by photomultiplier tubes. Two-phase detectors containing argon gas are used to detect the ionized electrons produced during the WIMP–nucleus scattering. As with most other liquefied noble gases, argon has a high scintillation light yield (about 51 photons/keV), is transparent to its own scintillation light, and is relatively easy to purify. Compared to xenon, argon is cheaper and has a distinct scintillation time profile, which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic beta-ray background is larger due to $^{39}$ Ar contamination, unless one uses argon from underground sources, which has much less $^{39}$ Ar contamination. Most of the argon in the Earth's atmosphere was produced by electron capture of long-lived $^{40}$ K ($^{40}$ K + e$^−$ → $^{40}$ Ar + ν) present in natural potassium within the Earth. The $^{39}$ Ar activity in the atmosphere is maintained by cosmogenic production through the knockout reaction $^{40}$ Ar(n,2n)$^{39}$ Ar and similar reactions. The half-life of $^{39}$ Ar is only 269 years. As a result, the underground Ar, shielded by rock and water, has much less $^{39}$ Ar contamination. Dark-matter detectors currently operating with liquid argon include DarkSide, WIMP Argon Programme (WArP), ArDM, Cryogenic Low-Energy Astrophysics with Neon (microCLEAN) and DEAP. Neutrino experiments include ICARUS and MicroBooNE, both of which use high-purity liquid argon in a time projection chamber for fine grained three-dimensional imaging of neutrino interactions.

## Solids

While argon is a gas at room temperature and pressure, it becomes a solid at liquid nitrogen temperature and melts to a liquid as in the image on the right when removed from the liquid nitrogen.

## Compounds

Argon fluorohydride (HArF), a compound of argon with fluorine and hydrogen that is stable below 17 K (−256.1 °C; −429.1 °F), has been demonstrated.

## Clathrates

Although the neutral ground-state chemical compounds of argon are presently limited to HArF, argon can form clathrates with water when atoms of argon are trapped in a lattice of water molecules.

## Atmospheres

Argon constitutes 0.934% by volume and 1.288% by mass of the Earth's atmosphere.

## Earth

The Earth's crust and seawater contain 1.2 ppm and 0.45 ppm of argon, respectively.

## Glaciology

"Nitrogen and argon isotopes in trapped air in Greenland ice show that the Greenland Summit warmed 9 ± 3°C over a period of several decades, beginning 14,672 years ago."

## Resources

* Chemicals/Actinides
* Chemicals/Aluminums
* Chemicals/Berylliums
* Chemicals/Leads
* Chemicals/Lithiums
* Chemicals/Nickels
* Chemicals/Thoriums