Argon

Formula: Ar
Molecular weight: 39.948
IUPAC Standard InChI: InChI=1S/Ar
IUPAC Standard InChIKey: XKRFYHLGVUSROY-UHFFFAOYSA-N
CAS Registry Number: 7440-37-1
Chemical structure:
This structure is also available as a 2d Mol file
Other names: Ar; UN 1006; UN 1951; argon atom
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Information on this page:
Other data available:
- Gas phase thermochemistry data
- Reaction thermochemistry data: reactions 1 to 50, reactions 51 to 100, reactions 101 to 102
- Ion clustering data
- Mass spectrum (electron ionization)
- Fluid Properties
Data at other public NIST sites:
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Phase change data

Go To: Top, Henry's Law data, Gas phase ion energetics data, References, Notes

Data compiled as indicated in comments:
TRC - Thermodynamics Research Center, NIST Boulder Laboratories, Chris Muzny director

Quantity	Value	Units	Method	Reference	Comment
T_boil	87.5	K	N/A	Streng, 1971	Uncertainty assigned by TRC = 0.3 K; TRC
T_boil	87.28	K	N/A	Gosman, McCarty, et al., 1969	Uncertainty assigned by TRC = 0.02 K; TRC
Quantity	Value	Units	Method	Reference	Comment
T_fus	83.8	K	N/A	Van't Zelfde, Omar, et al., 1968	Uncertainty assigned by TRC = 0.3 K; TRC
Quantity	Value	Units	Method	Reference	Comment
T_triple	87.78	K	N/A	Angus, Armstrong, et al., 1972	Uncertainty assigned by TRC = 0.05 K; TRC
T_triple	83.8	K	N/A	Gosman, McCarty, et al., 1969	Uncertainty assigned by TRC = 0.05 K; TRC
T_triple	83.8	K	N/A	Ziegler, Mullins, et al., 1962	Uncertainty assigned by TRC = 0.05 K; TRC
T_triple	83.78	K	N/A	Clark, Din, et al., 1951	Uncertainty assigned by TRC = 0.04 K; TRC
T_triple	83.78	K	N/A	Clusius and Weigand, 1940	Uncertainty assigned by TRC = 0.2 K; See property X for dP/dT at triple point; TRC
Quantity	Value	Units	Method	Reference	Comment
P_triple	0.689	bar	N/A	Gosman, McCarty, et al., 1969	Uncertainty assigned by TRC = 0.0001 bar; TRC
P_triple	0.689	bar	N/A	Ziegler, Mullins, et al., 1962	Uncertainty assigned by TRC = 0.0001 bar; TRC
P_triple	0.6875	bar	N/A	Clark, Din, et al., 1951	Uncertainty assigned by TRC = 0.0007 bar; TRC
Quantity	Value	Units	Method	Reference	Comment
T_c	150.86	K	N/A	Angus, Armstrong, et al., 1972	Uncertainty assigned by TRC = 0.1 K; TRC
T_c	150.86	K	N/A	Gosman, McCarty, et al., 1969	Uncertainty assigned by TRC = 0.1 K; TRC
T_c	150.65	K	N/A	McCain and Ziegler, 1967	Uncertainty assigned by TRC = 0.03 K; TRC
Quantity	Value	Units	Method	Reference	Comment
P_c	4.8979	bar	N/A	Angus, Armstrong, et al., 1972	Uncertainty assigned by TRC = 0.002 bar; TRC
P_c	48.9805	bar	N/A	Gosman, McCarty, et al., 1969	Uncertainty assigned by TRC = 0.1013 bar; TRC
P_c	48.5549	bar	N/A	McCain and Ziegler, 1967	Uncertainty assigned by TRC = 0.0709 bar; TRC
Quantity	Value	Units	Method	Reference	Comment
ρ_c	13.41	mol/l	N/A	Angus, Armstrong, et al., 1972	Uncertainty assigned by TRC = 0.005 mol/l; TRC
ρ_c	8.4029	mol/l	N/A	Gosman, McCarty, et al., 1969	Uncertainty assigned by TRC = 0.008 mol/l; TRC

Antoine Equation Parameters

log₁₀(P) = A − (B / (T + C))
P = vapor pressure (bar)
T = temperature (K)

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Temperature (K)	A	B	C	Reference	Comment
114.40 to 150.31	4.46903	481.012	22.156	McCain and Ziegler, 1967	Coefficents calculated by NIST from author's data.
83.78 to 150.72	3.29555	215.24	-22.233	Drii and Rabinovich, 1966	Coefficents calculated by NIST from author's data.
129.33 to 147.40	4.97171	658.982	49.819	van Itterbeek, Verbeke, et al., 1963	Coefficents calculated by NIST from author's data.
90.94 to 101.48	3.73479	302.683	-6.083	Clark, Din, et al., 1951, 2	Coefficents calculated by NIST from author's data.

In addition to the Thermodynamics Research Center (TRC) data available from this site, much more physical and chemical property data is available from the following TRC products:

Henry's Law data

Go To: Top, Phase change data, Gas phase ion energetics data, References, Notes

Data compiled by: Rolf Sander

Henry's Law constant (water solution)

k_H(T) = k°_H exp(d(ln(k_H))/d(1/T) ((1/T) - 1/(298.15 K)))
k°_H = Henry's law constant for solubility in water at 298.15 K (mol/(kg*bar))
d(ln(k_H))/d(1/T) = Temperature dependence constant (K)

k°_H (mol/(kg*bar))	d(ln(k_H))/d(1/T) (K)	Method	Reference
0.0014	1500.	L	N/A
0.0014	1100.	M	N/A

Gas phase ion energetics data

Go To: Top, Phase change data, Henry's Law data, References, Notes

Data evaluated as indicated in comments:
HL - Edward P. Hunter and Sharon G. Lias
L - Sharon G. Lias

Data compiled as indicated in comments:
LL - Sharon G. Lias and Joel F. Liebman
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron

Quantity	Value	Units	Method	Reference	Comment
IE (evaluated)	15.759 ± 0.001	eV	N/A	N/A	L
Quantity	Value	Units	Method	Reference	Comment
Proton affinity (review)	369.2	kJ/mol	N/A	Hunter and Lias, 1998	HL
Quantity	Value	Units	Method	Reference	Comment
Gas basicity	346.3	kJ/mol	N/A	Hunter and Lias, 1998	HL

Ionization energy determinations

IE (eV)	Method	Reference	Comment
15.763	PIPECO	Weitzel, Mahnert, et al., 1994	LL
15.75962	EVAL	Lide, 1992	LL
15.82	EI	Wetzel, Baiocchi, et al., 1987	LBLHLM
15.760	S	Kelly, 1987	LBLHLM
15.759	PE	Kimura, Katsumata, et al., 1981	LLK
15.88	EI	Clare and Sowerby, 1981	LLK
15.7	EI	Freiser, 1980	LLK
15.75962 ± 0.00001	S	Minnhagen, 1973	LLK
15.753 ± 0.002	TE	Spohr, Guyon, et al., 1971	LLK
15.75962 ± 0.00001	S	Yoshino, 1970	RDSH
15.759	S	Yoshino, 1969	RDSH
15.713 ± 0.003	CI	Hotop and Niehaus, 1969	RDSH
15.757 ± 0.005	PE	Collin and Natalis, 1968	RDSH
15.74 ± 0.05	EI	Gallegos and Klaver, 1967	RDSH
15.78 ± 0.03	EI	Winters, Collins, et al., 1966	RDSH
15.79	PE	Al-Joboury and Turner, 1963	RDSH

References

Go To: Top, Phase change data, Henry's Law data, Gas phase ion energetics data, Notes

Streng, 1971
Streng, A.G., Miscibility and Compatibility of Some Liquid and Solidified Gases at Low Temperature, J. Chem. Eng. Data, 1971, 16, 357. [all data]

Gosman, McCarty, et al., 1969
Gosman, A.L.; McCarty, R.D.; Hust, J.G., Thermodynamic Properties of Argon from the Triple Point to 300 K at Pressures to 1000 Atmospheres, Nat. Stand. Ref. Data Ser., Nat. Bur. Stand. NSRDS-NBS 27, 1969. [all data]

Van't Zelfde, Omar, et al., 1968
Van't Zelfde, P.; Omar, M.H.; LePair-Schroten, H.G.M.; Dokoupil, Z., Solid-liquid equilibrium diagram for the argon + methane system., Physica (Amsterdam), 1968, 38, 241-51. [all data]

Angus, Armstrong, et al., 1972
Angus, S.; Armstrong, B.; Gosman, A.L.; McCarty, R.D.; Hust, J.G.; Vasserman, A.A.; Rabinovich, V.A., International Thermodynamic Tables of the Fluid State - 1 Argon, Butterworths, London, 1972. [all data]

Ziegler, Mullins, et al., 1962
Ziegler, W.T.; Mullins, J.C.; Kirk, B.S., Calculation of the Vapor Pressure and Heats of Vaporization and Sublimation of Liquids and Solids, Especially Below One Atmosphere Pressure. II. Argon, Ga. Inst. Technol., Eng. Exp. Stn., Proj. A-460, Tech. Rep. No. 2, 1962. [all data]

Clark, Din, et al., 1951
Clark, A.M.; Din, F.; Robb, J.; Michels, A.; Wassenaar, T.; Zwietering, Th.N., The Vapor Pressure of Argon, Physica (Amsterdam), 1951, 17, 876. [all data]

Clusius and Weigand, 1940
Clusius, K.; Weigand, K., Melting Curves of the Gases A, Kr, Xe, CH4, CH3D, CD4, C2H4, C2H6, COS, and PH3 to 200 Atmospheres Pressure. The Chane of Volume on Melting, Z. Phys. Chem., Abt. B, 1940, 46, 1-37. [all data]

McCain and Ziegler, 1967
McCain, W.D., Jr.; Ziegler, W.T., The Critical Temperature, Critical Pressure, and Vapor Pressure of Argon, J. Chem. Eng. Data, 1967, 12, 2, 199-202, https://doi.org/10.1021/je60033a012 . [all data]

Drii and Rabinovich, 1966
Drii, L.I.; Rabinovich, V.A., Dependence of Vapor Pressure of Argon, Zh. Fiz. Khim., 1966, 40, 709-711. [all data]

van Itterbeek, Verbeke, et al., 1963
van Itterbeek, A.; Verbeke, O.; Staes, K., Measurements on the Equation of State of Liquid Argon and Methane Up to 300 kg cm^-2 at Low Temperatures, Physica (Amsterdam), 1963, 29, 6, 742-754, https://doi.org/10.1016/S0031-8914(63)80231-1 . [all data]

Clark, Din, et al., 1951, 2
Clark, A.M.; Din, F.; Robb, J.; Michels, A.; Wassenaar, T.; Zwietering, Th., The Vapour Pressure of Argon, Physica (Amsterdam), 1951, 17, 10, 876-884, https://doi.org/10.1016/0031-8914(51)90041-9 . [all data]

Hunter and Lias, 1998
Hunter, E.P.; Lias, S.G., Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update, J. Phys. Chem. Ref. Data, 1998, 27, 3, 413-656, https://doi.org/10.1063/1.556018 . [all data]

Weitzel, Mahnert, et al., 1994
Weitzel, K.-M.; Mahnert, J.; Penno, M., ZEKE-PEPICO investigations of dissociation energies in ionic reactions, Chem. Phys. Lett., 1994, 224, 371. [all data]

Lide, 1992
Lide, D.R. (Editor), Ionization potentials of atoms and atomic ions in Handbook of Chem. and Phys., 1992, 10-211. [all data]

Wetzel, Baiocchi, et al., 1987
Wetzel, R.C.; Baiocchi, F.A.; Hayes, T.R.; Freund, R.S., Absolute cross sections for electron-impact ionization of the rare-gas atoms by the fast-neutral-beam method, Phys. Rev. A, 1987, 35, 559. [all data]

Kelly, 1987
Kelly, R.L., Atomic and ionic spectrum lines of hydrogen through kryton, J. Phys. Chem. Ref. Data, 1987, 16. [all data]

Kimura, Katsumata, et al., 1981
Kimura, K.; Katsumata, S.; Achiba, Y.; Yamazaki, T.; Iwata, S., Ionization energies, Ab initio assignments, and valence electronic structure for 200 molecules in Handbook of HeI Photoelectron Spectra of Fundamental Organic Compounds, Japan Scientific Soc. Press, Tokyo, 1981. [all data]

Clare and Sowerby, 1981
Clare, P.; Sowerby, D.B., Electron impact ionisation energies of some halo-cyclotriphosphazenes, J. Inorg. Nucl. Chem., 1981, 43, 477. [all data]

Freiser, 1980
Freiser, B.S., Electron impact ionization of argon ions by trapped ion cyclotron resonanace spectroscopy, Int. J. Mass Spectrom. Ion Phys., 1980, 33, 263. [all data]

Minnhagen, 1973
Minnhagen, L., Spectrum and the energy levels of neutral argon, Ar I, J. Opt. Soc. Am., 1973, 63, 1185. [all data]

Spohr, Guyon, et al., 1971
Spohr, R.; Guyon, P.M.; Chupka, W.A.; Berkowitz, J., Threshold photoelectron detector for use in the vacuum ultraviolet, Rev. Sci. Instrum., 1971, 42, 1872. [all data]

Yoshino, 1970
Yoshino, K., Absorption spectrum of the argon atom in the vacuum-ultraviolet region, J. Opt. Soc. Am., 1970, 60, 1220. [all data]

Yoshino, 1969
Yoshino, K., Absorption spectrum of the argon atom in the vacuum-ultraviolet region, J. Opt. Soc. Am., 1969, 59, 1525. [all data]

Hotop and Niehaus, 1969
Hotop, H.; Niehaus, A., Reactions of excited atoms molecules with atoms and molecules. II. Energy analysis of penning electrons, Z. Phys., 1969, 228, 68. [all data]

Collin and Natalis, 1968
Collin, J.E.; Natalis, P., Vibrational and electronic ionic states of nitric oxide. An accurate method for measuring ionization potentials by photoelectron spectroscopy, Intern. J. Mass Spectrom. Ion Phys., 1968, 1, 483. [all data]

Gallegos and Klaver, 1967
Gallegos, E.J.; Klaver, R.F., Automatic voltage scanner for a peak switching mass spectrometer, J.Sci. Instr., 1967, 44, 427. [all data]

Winters, Collins, et al., 1966
Winters, R.E.; Collins, J.H.; Courchene, W.L., Resolution of fine structure in ionization-efficiency curves, J. Chem. Phys., 1966, 45, 1931. [all data]

Al-Joboury and Turner, 1963
Al-Joboury, M.I.; Turner, D.W., Molecular photo-electron spectroscopy. Part I. The hydrogen and nitrogen molecules, J. Chem. Soc., 1963, 5141. [all data]

Notes

Go To: Top, Phase change data, Henry's Law data, Gas phase ion energetics data, References

Symbols used in this document:

IE (evaluated)	Recommended ionization energy
P_c	Critical pressure
P_triple	Triple point pressure
T_boil	Boiling point
T_c	Critical temperature
T_fus	Fusion (melting) point
T_triple	Triple point temperature
d(ln(k_H))/d(1/T)	Temperature dependence parameter for Henry's Law constant
k°_H	Henry's Law constant at 298.15K
ρ_c	Critical density

Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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