Methyl fluoride

• Formula: CH₃F
• Molecular weight: 34.0329
• IUPAC Standard InChI: InChI=1S/CH3F/c1-2/h1H3 Copy

  
• IUPAC Standard InChIKey: NBVXSUQYWXRMNV-UHFFFAOYSA-N Copy
• CAS Registry Number: 593-53-3
• 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.
• Other names: Fluoromethane; Methane, fluoro-; Freon 41; CH3F; UN 2454; R 41; HFC-41; Refrigerant gas R 41
• 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
  • Reaction thermochemistry data
  • Henry's Law data
  • Gas phase ion energetics data
  • Ion clustering data
  • IR Spectrum
  • Mass spectrum (electron ionization)
  • Vibrational and/or electronic energy levels
  • Gas Chromatography
  • References
  • Notes
• Options:
  • Switch to SI units

Gas phase thermochemistry data

Go To: Top, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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:
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein

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.

View plot Requires a JavaScript / HTML 5 canvas capable browser.

View table.

Phase change data

Go To: Top, Gas phase thermochemistry data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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
BS - Robert L. Brown and Stephen E. Stein
AC - William E. Acree, Jr., James S. Chickos

Enthalpy of vaporization

Antoine Equation Parameters

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

View plot Requires a JavaScript / HTML 5 canvas capable browser.

Reaction thermochemistry data

Go To: Top, Gas phase thermochemistry data, Phase change data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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:
B - John E. Bartmess
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias
MS - José A. Martinho Simões
RCD - Robert C. Dunbar

Note: Please consider using the reaction search for this species. This page allows searching of all reactions involving this species. A general reaction search form is also available. Future versions of this site may rely on reaction search pages in place of the enumerated reaction displays seen below.

Individual Reactions

 +  = ( • )

By formula: Cl^- + CH₃F = (Cl^- • CH₃F)

CH₂F^- +  =

By formula: CH₂F^- + H⁺ = CH₃F

HO₂S⁺ +  = (HO₂S⁺ • )

By formula: HO₂S⁺ + CH₃F = (HO₂S⁺ • CH₃F)

 +  = ( • )

By formula: CH₃⁺ + CH₃F = (CH₃⁺ • CH₃F)

 +  = ( • )

By formula: Li⁺ + CH₃F = (Li⁺ • CH₃F)

CH₆N⁺ +  = (CH₆N⁺ • )

By formula: CH₆N⁺ + CH₃F = (CH₆N⁺ • CH₃F)

CH₄F⁺ +  = (CH₄F⁺ • )

By formula: CH₄F⁺ + CH₃F = (CH₄F⁺ • CH₃F)

C₅O₅W (g) +  (g) = C₆H₃FO₅W (g)

By formula: C₅O₅W (g) + CH₃F (g) = C₆H₃FO₅W (g)

 +  = ( • )

By formula: Al⁺ + CH₃F = (Al⁺ • CH₃F)

Henry's Law data

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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, Reaction thermochemistry data, Henry's Law data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, 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
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard

View reactions leading to CH₃F⁺ (ion structure unspecified)

Ionization energy determinations

Appearance energy determinations

De-protonation reactions

CH₂F^- +  =

By formula: CH₂F^- + H⁺ = CH₃F

Ion clustering data

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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:
RCD - Robert C. Dunbar
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias
B - John E. Bartmess

Note: Please consider using the reaction search for this species. This page allows searching of all reactions involving this species. Searches may be limited to ion clustering reactions. A general reaction search form is also available.

Clustering reactions

 +  = ( • )

By formula: Al⁺ + CH₃F = (Al⁺ • CH₃F)

 +  = ( • )

By formula: CH₃⁺ + CH₃F = (CH₃⁺ • CH₃F)

CH₄F⁺ +  = (CH₄F⁺ • )

By formula: CH₄F⁺ + CH₃F = (CH₄F⁺ • CH₃F)

CH₆N⁺ +  = (CH₆N⁺ • )

By formula: CH₆N⁺ + CH₃F = (CH₆N⁺ • CH₃F)

 +  = ( • )

By formula: Cl^- + CH₃F = (Cl^- • CH₃F)

HO₂S⁺ +  = (HO₂S⁺ • )

By formula: HO₂S⁺ + CH₃F = (HO₂S⁺ • CH₃F)

 +  = ( • )

By formula: Li⁺ + CH₃F = (Li⁺ • CH₃F)

IR Spectrum

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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

Data compiled by: NIST Mass Spectrometry Data Center, William E. Wallace, director

Gas Phase Spectrum

Notice: This spectrum may be better viewed with a Javascript and HTML 5 enabled browser.

For Zoom

1.) Enter the desired X axis range (e.g., 100, 200)

2.) Check here for automatic Y scaling

3.) Press here to zoom

Notice: Concentration information is not available for this spectrum and, therefore, molar absorptivity values cannot be derived.

Additional Data

Mass spectrum (electron ionization)

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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

Data compiled by: NIST Mass Spectrometry Data Center, William E. Wallace, director

Spectrum

Notice: This spectrum may be better viewed with a Javascript and HTML 5 enabled browser.

For Zoom

1.) Enter the desired X axis range (e.g., 100, 200)

2.) Check here for automatic Y scaling

3.) Press here to zoom

Additional Data

Vibrational and/or electronic energy levels

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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

Data compiled by: Takehiko Shimanouchi

Symmetry:   C_3ν     Symmetry Number σ = 3

Source: Shimanouchi, 1972

Notes

Gas Chromatography

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Site Links, NIST Free Links, NIST Subscription Links, References, Notes

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

Data compiled by: NIST Mass Spectrometry Data Center, William E. Wallace, director

Normal alkane RI, non-polar column, temperature ramp

View large format table.

Normal alkane RI, non-polar column, custom temperature program

View large format table.

References

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, Notes

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

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

Lias, Karpas, et al., 1985
Lias, S.G.; Karpas, Z.; Liebman, J.F., Halomethylenes: effects of halogen substitution on absolute heats of formation, J. Am. Chem. Soc., 1985, 107, 6089-6096. [all data]

Papousek, Tesar, et al., 1991
Papousek, D.; Tesar, R.; Pracna, P.; Civis, S.; Winnewisser, M.; Belov, S.P.; Tret'yakov, M.Y., High-resolution Fourier transform and submillimeter-wave study of the ν6 band of methyl-12C fluoride, J. Mol. Spectrosc., 1991, 147, 279-99. [all data]

PCR Inc., 1990
PCR Inc., Research Chemicals Catalog 1990-1991, PCR Inc., Gainesville, FL, 1990, 1. [all data]

Filatov, Makarov, et al., 1968
Filatov, A.S.; Makarov, S.P.; Yakubovich, A.Ya., Halogenation of 1,1,1-Trifluoroazomethane, Zh. Obshch. Khim., 1968, 38, 33. [all data]

Fonseca and Lobo, 1989
Fonseca, I.M.A.; Lobo, L.Q., Thermodynamics of liquid mixtures of xenon and methyl fluoride, Fluid Phase Equilib., 1989, 47, 249. [all data]

Bominaar, Biswas, et al., 1987
Bominaar, S.A.R.C.; Biswas, S.N.; Trappeniers, N.J.; Ten Seldam, C.A., (p, Vm, T) properties of methyl fluoride in the (gas + liquid) critical region, J. Chem. Thermodyn., 1987, 19, 959. [all data]

Cawood and Patterson, 1932
Cawood, W.; Patterson, H.S., Some Physical Constants of Methyl Fluoride, and the Atomic Weight of Fluorine, J. Chem. Soc., 1932, 1932, 2180. [all data]

Biswas, Ten Seldam, et al., 1989
Biswas, S.N.; Ten Seldam, C.A.; Bominaar, S.A.R.C.; Trappeniers, N.J., Liquid-vapor coexistence curve of methyl fluoride in the critical region, Fluid Phase Equilib., 1989, 49, 1-7. [all data]

Stephenson and Malanowski, 1987
Stephenson, Richard M.; Malanowski, Stanislaw, Handbook of the Thermodynamics of Organic Compounds, 1987, https://doi.org/10.1007/978-94-009-3173-2 . [all data]

Li and Rossini, 1961
Li, J.C.M.; Rossini, F.D., Vapor Pressures and Boiling Points of the l-Fluoroalkanes, l-Chloroalkanes, l-Bromoalkanes, and l-Iodoalkanes, C ₁ to C ₂₀ ., J. Chem. Eng. Data, 1961, 6, 2, 268-270, https://doi.org/10.1021/je60010a025 . [all data]

Dykyj, 1970
Dykyj, J., Petrochemica, 1970, 10, 2, 51. [all data]

Michels and Wassenaar, 1948
Michels, A.; Wassenaar, T., Vapour pressure of methylfluoride, Physica, 1948, 14, 2-3, 104-110, https://doi.org/10.1016/0031-8914(48)90030-5 . [all data]

Boublik, Fried, et al., 1984
Boublik, T.; Fried, V.; Hala, E., The Vapour Pressures of Pure Substances: Selected Values of the Temperature Dependence of the Vapour Pressures of Some Pure Substances in the Normal and Low Pressure Region, 2nd ed., Elsevier, New York, 1984, 972. [all data]

Moles and Batuecas, 1919
Moles, E.; Batuecas, T.J., J. Chim. Phys. Phys.-Chim. Biol., 1919, 17, 537. [all data]

Oi, Shulman, et al., 1983
Oi, Takao; Shulman, Jan; Popowicz, Anthony; Ishida, Takanobu, Vapor pressure isotope effects in liquid methyl fluoride, J. Phys. Chem., 1983, 87, 16, 3153-3160, https://doi.org/10.1021/j100239a038 . [all data]

Larson and McMahon, 1984
Larson, J.W.; McMahon, T.B., Hydrogen bonding in gas phase anions. An experimental investigation of the interaction between chloride ion and bronsted acids from ICR chloride exchange equilibria, J. Am. Chem. Soc., 1984, 106, 517. [all data]

Larson and McMahon, 1984, 2
Larson, J.W.; McMahon, T.B., Gas phase negative ion chemistry of alkylchloroformates, Can. J. Chem., 1984, 62, 675. [all data]

Rogers, Simpson, et al., 2010
Rogers, N.J.; Simpson, M.J.; Tuckett, R.P.; Dunn, K.F.; Latimer, C.J., Vacuum-UV negative photoion spectroscopy of CH3F, CH3Cl and CH3Br, Phys. Chem. Chem. Phys., 2010, 12, 36, 10971-10980, https://doi.org/10.1039/c0cp00234h . [all data]

Graul and Squires, 1990
Graul, S.T.; Squires, R.R., Gas-Phase Acidities Derived from Threshold Energies for Activated Reactions, J. Am. Chem. Soc., 1990, 112, 7, 2517, https://doi.org/10.1021/ja00163a007 . [all data]

McMahon and Kebarle, 1986
McMahon, T.B.; Kebarle, P., Strong hydrogen bonding in gas-phase ions: A high pressure mass spectrometric study of formation and energetics of methyl fluoride proton bound dimer, J. Am. Chem. Soc., 1986, 108, 6502. [all data]

McMahon, Heinis, et al., 1988
McMahon, T.; Heinis, T.; Nicol, G.; Hovey, J.K.; Kebarle, P., Methyl Cation Affinities, J. Am. Chem. Soc., 1988, 110, 23, 7591, https://doi.org/10.1021/ja00231a002 . [all data]

Foster, Williamson, et al., 1974
Foster, M.S.; Williamson, A.D.; Beauchamp, J.L., Photoionization mass spectrometry of trans-azomethane, Int. J. Mass Spectrom. Ion Phys., 1974, 15, 429. [all data]

Staley and Beauchamp, 1975
Staley, R.H.; Beauchamp, J.L., Intrinsic Acid - Base Properties of Molecules. Binding Energies of Li+ to pi - and n - Donor Bases, J. Am. Chem. Soc., 1975, 97, 20, 5920, https://doi.org/10.1021/ja00853a050 . [all data]

Dzidic and Kebarle, 1970
Dzidic, I.; Kebarle, P., Hydration of the Alkali Ions in the Gas Phase. Enthalpies and Entropies of Reactions M+(H2O)n-1 + H2O = M+(H2O)n, J. Phys. Chem., 1970, 74, 7, 1466, https://doi.org/10.1021/j100702a013 . [all data]

Meot-Ner, 1984
Meot-Ner, (Mautner)M., The Ionic Hydrogen Bond and Ion Solvation. 1. -NH+ O-, -NH+ N- and -OH+ O- Bonds. Correlations with Proton Affinity. Deviations Due to Structural Effects, J. Am. Chem. Soc., 1984, 106, 5, 1257, https://doi.org/10.1021/ja00317a015 . [all data]

Lias, Liebman, et al., 1984
Lias, S.G.; Liebman, J.F.; Levin, R.D., Evaluated gas phase basicities and proton affinities of molecules heats of formation of protonated molecules, J. Phys. Chem. Ref. Data, 1984, 13, 695. [all data]

Brown, Ishikawa, et al., 1990
Brown, C.E.; Ishikawa, Y.; Hackett, P.A.; Rayner, D.M., J. Am. Chem. Soc., 1990, 112, 2530. [all data]

Bouchard, Brenner, et al., 1997
Bouchard, F.; Brenner, V.; Carra, C.; Hepburn, J.W.; Koyanagi, G.K.; McMahon, T.B.; Ohanessian, G.; Peschke, M., Energetics and Structure of Complexes of Al+ with Small Organic Molecules in the Gas Phase, J. Phys. Chem. A, 1997, 101, 33, 5885, https://doi.org/10.1021/jp9703465 . [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]

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, Asbrink, et al., 1981
Bieri, G.; Asbrink, L.; Von Niessen, W., 30.4 nm He(II) photoelectron spectra of organic molecules. Part IV. Fluoro-compounds (C,H,F), J. Electron Spectrosc. Relat. Phenom., 1981, 23, 281. [all data]

Brundle, Robin, et al., 1970
Brundle, C.R.; Robin, M.B.; Basch, H., Electronic energies and electronic structures of the fluoromethanes, J. Chem. Phys., 1970, 53, 2196. [all data]

Krauss, Walker, et al., 1968
Krauss, M.; Walker, J.A.; Dibeler, V.H., Mass spectrometric study of photoionization. X. Hydrogen chloride and methyl halides, J. Res. NBS, 1968, 72A, 281. [all data]

Uehara, Saito, et al., 1973
Uehara, Y.; Saito, N.; Yonezawa, T., Ionization potentials of trifluoromethyl and methyl halides by photoelectron spectroscopy and calculations by extended Hucket and CNDO/2 methods, Chem. Lett., 1973, 495. [all data]

Harshbarger, Robin, et al., 1973
Harshbarger, W.R.; Robin, M.B.; Lassettre, E.N., The electron impact spectra of the fluoromethanes, J. Electron Spectrosc. Relat. Phenom., 1973, 1, 319. [all data]

Holmes, Lossing, et al., 1983
Holmes, J.L.; Lossing, F.P.; Terlouw, J.K.; Burgers, P.C., Novel gas-phase ions. The radical cations [CH₂XH]⁺. (X = F, Cl, Br, I, OH, NH², SH) and [CH₂CH₂NH₃]⁺., Can. J. Chem., 1983, 61, 2305. [all data]

Martin, Lampe, et al., 1966
Martin, R.H.; Lampe, F.W.; Taft, R.W., An electron-impact study of ionization and dissociation in methoxy- and halogen- substituted methanes, J. Am. Chem. Soc., 1966, 88, 1353. [all data]

Shimanouchi, 1972
Shimanouchi, T., Tables of Molecular Vibrational Frequencies Consolidated Volume I, National Bureau of Standards, 1972, 1-160. [all data]

Zenkevich, 2005
Zenkevich, I.G., Experimentally measured retention indices., 2005. [all data]

Zenkevich and Rodin, 2004
Zenkevich, I.G.; Rodin, A.A., Gas chromatographic identification of some volatile toxic fluorine containing compounds by precalculated retention indices, J. Ecol. Chem. (Rus.), 2004, 13, 1, 22-28. [all data]

Notes

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, IR Spectrum, Mass spectrum (electron ionization), Vibrational and/or electronic energy levels, Gas Chromatography, Site Links, NIST Free Links, NIST Subscription Links, 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)
  Tboil	Boiling point
  Tc	Critical temperature
  d(ln(kH))/d(1/T)	Temperature dependence parameter for Henry's Law constant
  k°H	Henry's Law constant at 298.15K
  ΔfH°gas	Enthalpy of formation of gas at standard conditions
  ΔrG°	Free energy of reaction at standard conditions
  ΔrH°	Enthalpy of reaction at standard conditions
  ΔrS°	Entropy of reaction at standard conditions
  ΔvapH	Enthalpy of vaporization
  ρc	Critical density

• Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
• The National Institute of Standards and Technology (NIST) uses its best efforts to deliver a high quality copy of the Database and to verify that the data contained therein have been selected on the basis of sound scientific judgment. However, NIST makes no warranties to that effect, and NIST shall not be liable for any damage that may result from errors or omissions in the Database.
• Customer support for NIST Standard Reference Data products.