Hydrogen

• Formula: H₂
• Molecular weight: 2.01588
• IUPAC Standard InChI: InChI=1S/H2/h1H Copy

  
• IUPAC Standard InChIKey: UFHFLCQGNIYNRP-UHFFFAOYSA-N Copy
• CAS Registry Number: 1333-74-0
• Chemical structure:
  This structure is also available as a 2d Mol file or as a computed 3d SD file
  The 3d structure may be viewed using Java or Javascript.
• Isotopologues:
  • tritium
  • deuterium hydride
  • Deuterium
• Other names: Dihydrogen; o-Hydrogen; p-Hydrogen; Molecular hydrogen; H2; UN 1049; UN 1966
• Permanent link for this species. Use this link for bookmarking this species for future reference.
• Information on this page:
  • Gas phase thermochemistry data
  • Phase change data
  • Henry's Law data
  • Gas phase ion energetics data
  • References
  • Notes
• Other data available:
  • Reaction thermochemistry data: reactions 1 to 50, reactions 51 to 100, reactions 101 to 150, reactions 151 to 200, reactions 201 to 250, reactions 251 to 300, reactions 301 to 350, reactions 351 to 400, reactions 401 to 450, reactions 451 to 500, reactions 501 to 550, reactions 551 to 600, reactions 601 to 621
  • Ion clustering data
  • Mass spectrum (electron ionization)
  • Constants of diatomic molecules
  • Fluid Properties
• Data at other public NIST sites:
  • Electron-Impact Ionization Cross Sections (on physics web site)
  • Gas Phase Kinetics Database
• Options:
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Gas phase thermochemistry data

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

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Gas Phase Heat Capacity (Shomate Equation)

C_p° = A + B*t + C*t² + D*t³ + E/t²
H° − H°_298.15= A*t + B*t²/2 + C*t³/3 + D*t⁴/4 − E/t + F − H
S° = A*ln(t) + B*t + C*t²/2 + D*t³/3 − E/(2*t²) + G
    C_p = heat capacity (cal/mol*K)
    H° = standard enthalpy (kcal/mol)
    S° = standard entropy (cal/mol*K)
    t = temperature (K) / 1000.

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View table.

Phase change data

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Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

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

Antoine Equation Parameters

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

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Henry's Law data

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Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

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)

Gas phase ion energetics data

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

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

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

Data compiled as indicated in comments:
B - John E. Bartmess
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

View reactions leading to H₂⁺ (ion structure unspecified)

Ionization energy determinations

Appearance energy determinations

De-protonation reactions

 +  =

By formula: H^- + H⁺ = H₂

References

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

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Cox, Wagman, et al., 1984
Cox, J.D.; Wagman, D.D.; Medvedev, V.A., CODATA Key Values for Thermodynamics, Hemisphere Publishing Corp., New York, 1984, 1. [all data]

Chase, 1998
Chase, M.W., Jr., NIST-JANAF Themochemical Tables, Fourth Edition, J. Phys. Chem. Ref. Data, Monograph 9, 1998, 1-1951. [all data]

Roder, Childs, et al., 1973
Roder, H.M.; Childs, G.E.; McCarty, R.D.; Angerhofer, P.E., Survey of the Prop. of the Hydrogen Isotopes Below Their Critical Temp, Natl. Bur. Stand. (U. S.), 1973. [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]

Henning and Otto, 1936
Henning, F.; Otto, J., Vapor pressure curves and triple points in the temperature region from 14 to 90 k, Phys. Z., 1936, 37, 633-8. [all data]

Onnes, Crommelin, et al., 1917
Onnes, H.K.; Crommelin, C.-A.; Cath, P.G., Isothermals of di-atomic substances and their binary mixtures. XIX. A preliminary determination of the critical point of hydrogen., Proc. K. Ned. Akad. Wet., 1917, 20, 178-184. [all data]

van Itterbeek, Verbeke, et al., 1964
van Itterbeek, A.; Verbeke, O.; Theewes, F.; Staes, K.; de Boelpaep, J., The Difference in Vapour Pressure Between Normal and Equilibrium Hydrogen. Vapour Pressure of Normal Hydrogen Between 20 ºK and 32 ºK, Physica (Amsterdam), 1964, 30, 6, 1238-1244, https://doi.org/10.1016/0031-8914(64)90114-4 . [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]

Shiner, Gilligan, et al., 1993
Shiner, D.; Gilligan, J.M.; Cook, B.M.; Lichten, W., H₂, D₂, and HD ionization potentials by accurate calibration of several iodine lines, Phys. Rev. A, 1993, 47, 4042. [all data]

McCormack, Gilligan, et al., 1989
McCormack, E.; Gilligan, J.M.; Cornaggia, C.; Eyler, E.E., Measurement of high Rydberg states and the ionization potential of H₂, Phys. Rev. A, 1989, 39, 2260. [all data]

Glab and Hessler, 1987
Glab, W.L.; Hessler, J.P., Multiphoton excitation of high singlet np Rydberg states of molecular hydrogen: Spectroscopy and dynamics, Phys. Rev. A, 1987, 35, 2102. [all data]

Eyler, Short, et al., 1986
Eyler, E.E.; Short, R.C.; Pipkin, F.M., Precision spectroscopy of the nf triplet Rydberg states of H₂ and determination of the triplet ionization potential, Phys. Rev. Lett., 1986, 56, 2602. [all data]

Farber, Srivastava, et al., 1982
Farber, M.; Srivastava, R.D.; Moyer, J.W., Mass spectrometric determination of the thermodynamics of potassium hydroxide and minor potassium-containing species required in magnetohydrodynamic power systems, J. Chem. Thermodyn., 1982, 14, 1103. [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]

Bieri, Schmelzer, et al., 1980
Bieri, G.; Schmelzer, A.; Asbrink, L.; Jonsson, M., Fluorine and the fluoroderivatives of acetylene and diacetylene studied by 30.4 nm He(II) photoelectron spectroscopy, Chem. Phys., 1980, 49, 213. [all data]

Huber and Herzberg, 1979
Huber, K.P.; Herzberg, G., Molecular Spectra and Molecular Structure. IV. Constants of Diatomic Molecules,, Van Nostrand Reinhold Co., 1979, ,1. [all data]

Farber and Srivastava, 1977
Farber, M.; Srivastava, R.D., Mass spectrometric determination of the heats of formation of the silane fluorides, Chem. Phys. Lett., 1977, 51, 307. [all data]

Rabalais, Debies, et al., 1974
Rabalais, J.W.; Debies, T.P.; Berkosky, J.L.; Huang, J.-T.J.; Ellison, F.O., Calculated photoionization cross sections relative experimental photoionization intensities for a selection of small molecules, J. Chem. Phys., 1974, 61, 516. [all data]

Lee and Rabalais, 1974
Lee, T.H.; Rabalais, J.W., Vibrational transition probabilities in photoelectron spectra, J. Chem. Phys., 1974, 61, 2747. [all data]

Herzberg and Jungen, 1972
Herzberg, G.; Jungen, Ch., Rydberg series and ionization potential of the H₂ molecule, J. Mol. Spectrosc., 1972, 41, 425. [all data]

Takezawa, 1970
Takezawa, S., Absorption spectrum of H₂ in the vacuum-uv region. II. Rydberg series converging to the first six vibrational levels of the H₂⁺ ground state, J. Chem. Phys., 1970, 52, 5793. [all data]

Asbrink, 1970
Asbrink, L., The photoelectron spectrum of H₂, Chem. Phys. Lett., 1970, 7, 549. [all data]

Lossing and Semeluk, 1969
Lossing, F.P.; Semeluk, G.P., Threshold ionization efficiency curves for monoenergetic electron impact on H₂, D₂, CH₄ and CD₄, Intern. J. Mass Spectrom. Ion Phys., 1969, 2, 408. [all data]

Herzberg, 1969
Herzberg, G., Dissociation energy and ionization potential of molecular hydrogen, Phys. Rev. Letters, 1969, 23, 1081. [all data]

Villarejo, 1968
Villarejo, D., Measurement of threshold electrons in the photoionization of H₂ and D₂, J. Chem. Phys., 1968, 48, 4014. [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]

Cermak, 1968
Cermak, V., Penning ionization electron spectroscopy. I. Determination of ionization potentials of polyatomic molecules, Collection Czech. Chem. Commun., 1968, 33, 2739. [all data]

Kerwin, Marmet, et al., 1963
Kerwin, L.; Marmet, P.; Clarke, E.M., Recent work with the electrostatic electron selector, Advan. Mass Spectrom., 1963, 2, 522. [all data]

Beutler and Junger, 1936
Beutler, H.; Junger, H.-O., Uber das Absorptionsspektrum des Wasserstoffs. III. Die Autoionisierung im Term 3pπ 1u des H₂ und ihre Auswahlgesetze. Bestimmung der lonisierungsenergie des H₂, Z. Physik, 1936, 100, 80. [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]

Crowe and McConkey, 1973
Crowe, A.; McConkey, J.W., Dissociative ionization by electron impact. I. Protons from H₂, J. Phys. B:, 1973, 6, 2088. [all data]

Locht and Momigny, 1971
Locht, R.; Momigny, J., Mass spectrometric study of ion-pair processes in diatomic molecules: H₂, CO, NO and O₂, Int. J. Mass Spectrom. Ion Phys., 1971, 7, 121. [all data]

Curran, Laboratories
Curran, R.K., Negative ion formation in various gases at pressures up to .5 mm of Hg, Scientific Paper 62-908-113-P7, Westinghouse Research, Laboratories, Pittsburgh, 1962. [all data]

Shiell, Hu, et al., 2000
Shiell, R.C.; Hu, X.K.; Hu, Q.C.J.; Hepburn, J.W., Threshold Ion-pair Production spectroscopy (TIPPS) of H2 and D2, Faraday Disc. Chem. Soc., 2000, 115, 331, https://doi.org/10.1039/a909428h . [all data]

Pratt, McCormack, et al., 1992
Pratt, S.T.; McCormack, E.F.; Dehmer, J.L.; Dehmer, P.M., Field-Induced Ion-Pair Formation in Molecular Hydrogen, Phys. Rev. Lett., 1992, 68, 5, 584, https://doi.org/10.1103/PhysRevLett.68.584 . [all data]

Gurvich, Veyts, et al.
Gurvich, L.V.; Veyts, I.V.; Alcock, C.B., Hemisphere Publishing, NY, 1989, V. 1 2, Thermodynamic Properties of Individual Substances, 4th Ed. [all data]

Lykke, Murray, et al., 1991
Lykke, K.R.; Murray, K.K.; Lineberger, W.C., Threshold Photodetachment of H-, Phys. Rev. A, 1991, 43, 11, 6104, https://doi.org/10.1103/PhysRevA.43.6104 . [all data]

Notes

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

• Symbols used in this document:
  

  AE	Appearance energy
  IE (evaluated)	Recommended ionization energy
  Pc	Critical pressure
  Ptriple	Triple point pressure
  S°gas,1 bar	Entropy of gas at standard conditions (1 bar)
  Tc	Critical temperature
  Ttriple	Triple point temperature
  d(ln(kH))/d(1/T)	Temperature dependence parameter for Henry's Law constant
  k°H	Henry's Law constant at 298.15K
  ΔrG°	Free energy of reaction at standard conditions
  ΔrH°	Enthalpy of reaction at standard conditions
  ρc	Critical density

• Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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