Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid or gas.[1]


Argon emission spectrum has enhanced lines. Credit: Abilanin.{{free media}}

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.[2]

Argon has an emission line occurring in the solar corona at 553.6 nm from Ar X.[3]

Argon has an emission line that occurs in an electron cyclotron resonance (ECR) heated plasmas: 473.591 nm from Ar II.[2]

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.[2]


Argon spectrum is 400 nm - 700 nm. Credit: McZusatz.{{free media}}


Spectrum of an argon discharge tube in the 520-1100nm range. Credit: Umop503.{{free media}}

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.


This shows an Argon spectra using a 600lpm diffraction grating. Credit: teravolt.{{free media}}

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.[2]


Spectrum = gas discharge tube: the noble gas: argon Ar, used with 1.8 kV, 18 mA, 35 kHz. ≈ 8" length.Alchemist-hp.{{free media}}

Argon is a noble gas.


Liquid argon drips off of a small block of solid argon. Credit: Fir0002.{{free media}}

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[4]), 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
contamination, unless one uses argon from underground sources, which has much less 39
contamination. Most of the argon in the Earth's atmosphere was produced by electron capture of long-lived 40
+ e40
+ ν) present in natural potassium within the Earth. The 39
activity in the atmosphere is maintained by cosmogenic production through the knockout reaction 40
and similar reactions. The half-life of 39
is only 269 years. As a result, the underground Ar, shielded by rock and water, has much less 39
contamination.[5] 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.


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.


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.[6][7]


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.[8]


Argon constitutes 0.934% by volume and 1.288% by mass of the Earth's atmosphere.[9]


The Earth's crust and seawater contain 1.2 ppm and 0.45 ppm of argon, respectively.[10]


"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."[11]


See alsoEdit


  1. "Material Safety Data Sheet Gaseous Argon". Universal Industrial Gases, Inc. Retrieved 14 October 2013.
  2. 2.0 2.1 2.2 2.3 K. J. McCarthy; A. Baciero; B. Zurro; TJ-II Team (12 June 2000). Impurity Behaviour Studies in the TJ-II Stellarator, In: 27th EPS Conference on Contr. Fusion and Plasma Phys.. 24B. Budapest: ECA. pp. 1244-7. Retrieved 20 January 2013. 
  3. P. Swings (July 1943). "Edlén's Identification of the Coronal Lines with Forbidden Lines of Fe X, XI, XIII, XIV, XV; Ni XII, XIII, XV, XVI; Ca XII, XIII, XV; a X, XIV". The Astrophysical Journal 98 (07): 116-28. doi:10.1086/144550. 
  4. Gastler, Dan; Kearns, Ed; Hime, Andrew; Stonehill, Laura C. et al. (2012). "Measurement of scintillation efficiency for nuclear recoils in liquid argon". Physical Review C 85 (6): 065811. doi:10.1103/PhysRevC.85.065811. 
  5. Xu, J.; Calaprice, F.; Galbiati, C.; Goretti, A.; Guray, G. (26 April 2012). "A Study of the Residual 39
    Content in Argon from Underground Sources". Astroparticle Physics 66 (2015): 53–60. doi:10.1016/j.astropartphys.2015.01.002.
  6. Khriachtchev, Leonid; Pettersson, Mika; Runeberg, Nino; Lundell, Jan; Räsänen, Markku (2000). "A stable argon compound". Nature 406 (6798): 874–876. doi:10.1038/35022551. PMID 10972285. 
  7. Perkins, S. (26 August 2000). "HArF! Argon's not so noble after all – researchers make argon fluorohydride". Science News.
  8. Belosludov, V. R.; Subbotin, O. S.; Krupskii, D. S.; Prokuda, O. V.; Belosludov, R. V.; Kawazoe, Y. (2006). "Microscopic model of clathrate compounds". Journal of Physics: Conference Series 29 (1): 1–7. doi:10.1088/1742-6596/29/1/001. 
  9. "Argon (Ar)". Encyclopædia Britannica. Retrieved on 14 January 2014.
  10. Emsley, J. (2001). Nature's Building Blocks. Oxford University Press. pp. 44–45. 
  11. Jeffrey P. Severinghaus; Edward J. Brook (29 October 1999). "Abrupt Climate Change at the End of the Last Glacial Period Inferred from Trapped Air in Polar Ice". Science 286 (5441): 930-4. Retrieved 2014-10-01.