Formyl cation


Reaction thermochemistry 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: Michael M. Meot-Ner (Mautner) and Sharon G. Lias

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

Formyl cation + Carbon monoxide = (Formyl cation • Carbon monoxide)

By formula: CHO+ + CO = (CHO+ • CO)

Quantity Value Units Method Reference Comment
Δr10.8kcal/molPHPMSJennings, Headley, et al., 1982gas phase
Δr12.8kcal/molPHPMSHiraoka, Saluja, et al., 1979gas phase
Δr11.7kcal/molPHPMSMeot-Ner (Mautner) and Field, 1974gas phase
Quantity Value Units Method Reference Comment
Δr22.5cal/mol*KPHPMSJennings, Headley, et al., 1982gas phase
Δr24.cal/mol*KPHPMSHiraoka, Saluja, et al., 1979gas phase
Δr20.9cal/mol*KPHPMSMeot-Ner (Mautner) and Field, 1974gas phase

(Formyl cation • 2Carbon monoxide) + Carbon monoxide = (Formyl cation • 3Carbon monoxide)

By formula: (CHO+ • 2CO) + CO = (CHO+ • 3CO)

Quantity Value Units Method Reference Comment
Δr4.7 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Δr6.3kcal/molPHPMSHiraoka, Saluja, et al., 1979gas phase
Quantity Value Units Method Reference Comment
Δr15.8cal/mol*KPHPMSHiraoka and Mori, 1989gas phase
Δr26.cal/mol*KPHPMSHiraoka, Saluja, et al., 1979gas phase

(Formyl cation • 3Carbon monoxide) + Carbon monoxide = (Formyl cation • 4Carbon monoxide)

By formula: (CHO+ • 3CO) + CO = (CHO+ • 4CO)

Quantity Value Units Method Reference Comment
Δr4.5 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Δr6.2kcal/molPHPMSHiraoka, Saluja, et al., 1979gas phase
Quantity Value Units Method Reference Comment
Δr18.2cal/mol*KPHPMSHiraoka and Mori, 1989gas phase
Δr29.cal/mol*KPHPMSHiraoka, Saluja, et al., 1979gas phase

(Formyl cation • 4Carbon monoxide) + Carbon monoxide = (Formyl cation • 5Carbon monoxide)

By formula: (CHO+ • 4CO) + CO = (CHO+ • 5CO)

Quantity Value Units Method Reference Comment
Δr4.2 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Δr5.8kcal/molPHPMSHiraoka, Saluja, et al., 1979gas phase
Quantity Value Units Method Reference Comment
Δr22.9cal/mol*KPHPMSHiraoka and Mori, 1989gas phase
Δr32.cal/mol*KPHPMSHiraoka, Saluja, et al., 1979gas phase

(Formyl cation • Carbon monoxide) + Carbon monoxide = (Formyl cation • 2Carbon monoxide)

By formula: (CHO+ • CO) + CO = (CHO+ • 2CO)

Quantity Value Units Method Reference Comment
Δr4.9 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Δr6.6kcal/molPHPMSHiraoka, Saluja, et al., 1979gas phase
Quantity Value Units Method Reference Comment
Δr15.0cal/mol*KPHPMSHiraoka and Mori, 1989gas phase
Δr24.cal/mol*KPHPMSHiraoka, Saluja, et al., 1979gas phase

(Formyl cation • 14Carbon monoxide) + Carbon monoxide = (Formyl cation • 15Carbon monoxide)

By formula: (CHO+ • 14CO) + CO = (CHO+ • 15CO)

Quantity Value Units Method Reference Comment
Δr1.76kcal/molPHPMSHiraoka and Mori, 1989gas phase; Entropy change calculated or estimated
Quantity Value Units Method Reference Comment
Δr23.cal/mol*KN/AHiraoka and Mori, 1989gas phase; Entropy change calculated or estimated

(Formyl cation • 3Carbon dioxide) + Carbon dioxide = (Formyl cation • 4Carbon dioxide)

By formula: (CHO+ • 3CO2) + CO2 = (CHO+ • 4CO2)

Quantity Value Units Method Reference Comment
Δr8.4kcal/molPHPMSHiraoka, Shoda, et al., 1986gas phase; Entropy change calculated or estimated
Quantity Value Units Method Reference Comment
Δr24.cal/mol*KN/AHiraoka, Shoda, et al., 1986gas phase; Entropy change calculated or estimated

(Formyl cation • 10Carbon monoxide) + Carbon monoxide = (Formyl cation • 11Carbon monoxide)

By formula: (CHO+ • 10CO) + CO = (CHO+ • 11CO)

Quantity Value Units Method Reference Comment
Δr2.0 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr23.0cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 11Carbon monoxide) + Carbon monoxide = (Formyl cation • 12Carbon monoxide)

By formula: (CHO+ • 11CO) + CO = (CHO+ • 12CO)

Quantity Value Units Method Reference Comment
Δr1.9 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr23.2cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 12Carbon monoxide) + Carbon monoxide = (Formyl cation • 13Carbon monoxide)

By formula: (CHO+ • 12CO) + CO = (CHO+ • 13CO)

Quantity Value Units Method Reference Comment
Δr1.8 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr23.2cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 13Carbon monoxide) + Carbon monoxide = (Formyl cation • 14Carbon monoxide)

By formula: (CHO+ • 13CO) + CO = (CHO+ • 14CO)

Quantity Value Units Method Reference Comment
Δr1.8 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr23.1cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 9Carbon monoxide) + Carbon monoxide = (Formyl cation • 10Carbon monoxide)

By formula: (CHO+ • 9CO) + CO = (CHO+ • 10CO)

Quantity Value Units Method Reference Comment
Δr2.0 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr22.3cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 5Carbon monoxide) + Carbon monoxide = (Formyl cation • 6Carbon monoxide)

By formula: (CHO+ • 5CO) + CO = (CHO+ • 6CO)

Quantity Value Units Method Reference Comment
Δr2.4 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr19.0cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 6Carbon monoxide) + Carbon monoxide = (Formyl cation • 7Carbon monoxide)

By formula: (CHO+ • 6CO) + CO = (CHO+ • 7CO)

Quantity Value Units Method Reference Comment
Δr2.3 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr21.1cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 7Carbon monoxide) + Carbon monoxide = (Formyl cation • 8Carbon monoxide)

By formula: (CHO+ • 7CO) + CO = (CHO+ • 8CO)

Quantity Value Units Method Reference Comment
Δr2.2 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr22.0cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 8Carbon monoxide) + Carbon monoxide = (Formyl cation • 9Carbon monoxide)

By formula: (CHO+ • 8CO) + CO = (CHO+ • 9CO)

Quantity Value Units Method Reference Comment
Δr2.1 ± 0.3kcal/molPHPMSHiraoka and Mori, 1989gas phase
Quantity Value Units Method Reference Comment
Δr22.6cal/mol*KPHPMSHiraoka and Mori, 1989gas phase

(Formyl cation • 2Carbon dioxide) + Carbon dioxide = (Formyl cation • 3Carbon dioxide)

By formula: (CHO+ • 2CO2) + CO2 = (CHO+ • 3CO2)

Quantity Value Units Method Reference Comment
Δr6.9kcal/molPHPMSHiraoka, Shoda, et al., 1986gas phase
Quantity Value Units Method Reference Comment
Δr22.7cal/mol*KPHPMSHiraoka, Shoda, et al., 1986gas phase

(Formyl cation • Carbon dioxide) + Carbon dioxide = (Formyl cation • 2Carbon dioxide)

By formula: (CHO+ • CO2) + CO2 = (CHO+ • 2CO2)

Quantity Value Units Method Reference Comment
Δr7.2kcal/molPHPMSHiraoka, Shoda, et al., 1986gas phase
Quantity Value Units Method Reference Comment
Δr19.7cal/mol*KPHPMSHiraoka, Shoda, et al., 1986gas phase

Formyl cation + Hydrogen = (Formyl cation • Hydrogen)

By formula: CHO+ + H2 = (CHO+ • H2)

Quantity Value Units Method Reference Comment
Δr3.9kcal/molPHPMSHiraoka and Kebarle, 1975gas phase
Quantity Value Units Method Reference Comment
Δr20.5cal/mol*KPHPMSHiraoka and Kebarle, 1975gas phase

Formyl cation + Carbon dioxide = (Formyl cation • Carbon dioxide)

By formula: CHO+ + CO2 = (CHO+ • CO2)

Quantity Value Units Method Reference Comment
Δr12.6kcal/molPHPMSHiraoka, Shoda, et al., 1986gas phase
Quantity Value Units Method Reference Comment
Δr21.4cal/mol*KPHPMSHiraoka, Shoda, et al., 1986gas phase

Vibrational and/or electronic energy levels

Go To: Top, Reaction thermochemistry data, 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: Marilyn E. Jacox

State:   X


Vib. 
sym. 
 No.   Approximate 
 type of mode 
 cm-1   Med.   Method   References

Σ+ 1 CH stretch 3088.74 gas LD CC Gudeman, Begemann, et al., 1983
Amano, 1983
Owrutsky, Keim, et al., 1989
Keim, Polak, et al., 1990
1 CH stretch 3076.31 H gas PF Nizkorodov, Maier, et al., 1995
1 CH stretch 3046.12 gas PF Nizkorodov, Dopfer, et al., 1996
1 CH stretch 2815.06 A gas PF Nizkorodov, Dopfer, et al., 1995
1 CH stretch 2840 H gas PF Bieske, Nizkorodov, et al., 1995
Π 2 Bend 829.72 gas DL MPI Davies and Rothwell, 1984
Kawaguchi, Yamada, et al., 1985
Foltynowicz, Robinson, et al., 2000
Σ+ 3 CO stretch 2183.95 gas DL Foster, McKellar, et al., 1984
Davies, Hamilton, et al., 1984
Liu, Lee, et al., 1988
3 CO stretch 2135.71 A gas DL Linnartz, Speck, et al., 1998

Additional references: Jacox, 1994, page 37; Jacox, 1998, page 145; Jacox, 2003, page 33; Dyke, Jonathan, et al., 1980; Bogey, Demuynck, et al., 1981; Sastry, Herbst, et al., 1981; Woods, Saykally, et al., 1981; Foster and McKellar, 1984; Kawaguchi, McKellar, et al., 1986; Dyke, 1987; Woods, 1988; Ohshima, Sumiyoshi, et al., 1997; Olkhov, Nizkorodov, et al., 1997; Foltynowicz, Robinson, et al., 2001; Foltynowicz, Robinson, et al., 2001, 2; Dore, Beninati, et al., 2003

Notes

H(1/2)(2ν)
A0~1 cm-1 uncertainty

References

Go To: Top, Reaction thermochemistry data, Vibrational and/or electronic energy levels, Notes

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

Jennings, Headley, et al., 1982
Jennings, K.R.; Headley, J.V.; Mason, R.S., The Temperature Dependence of Ion - Molecule Association Reactions, Int. J. Mass. Spectrom. Ion Phys, 1982, 45, 315. [all data]

Hiraoka, Saluja, et al., 1979
Hiraoka, K.; Saluja, P.P.S.; Kebarle, P., Stabilities of Complexes (N2)nH+, (CO)nH+ and (O2)nH+ for n = 1 to 7 Based on Gas Phase Ion Equilibrium Measurements, Can. J. Chem., 1979, 57, 16, 2159, https://doi.org/10.1139/v79-346 . [all data]

Meot-Ner (Mautner) and Field, 1974
Meot-Ner (Mautner), M.; Field, F.H., Kinetics and Thermodynamics of the Association of CO+ with CO and of N2+ with N2 between 120 and 650 K, J. Chem. Phys., 1974, 61, 9, 3742, https://doi.org/10.1063/1.1682560 . [all data]

Hiraoka and Mori, 1989
Hiraoka, K.; Mori, T., Gas Phase Stabilities of the Cluster Ions H+(CO)2(CO)n, H+(N2)2(N2)n and H+(O2)2(O2)n with n = 1 - 14, Chem. Phys., 1989, 137, 1-3, 345, https://doi.org/10.1016/0301-0104(89)87119-8 . [all data]

Hiraoka, Shoda, et al., 1986
Hiraoka, K.; Shoda, T.; Morise, K.; Yamabe, S.; Kawai, E.; Hirao, K., Stability and structure of cluster ions in the gas phase: Carbon dioxide with Cl-, H3O+, HCO2+ and HCO+, J. Chem. Phys., 1986, 84, 2091. [all data]

Hiraoka and Kebarle, 1975
Hiraoka, K.; Kebarle, P., Stability and Structure of H3CO+ Formed from COH+ + H2 at Low Temperature, J. Chem. Phys., 1975, 63, 4, 1688, https://doi.org/10.1063/1.431499 . [all data]

Gudeman, Begemann, et al., 1983
Gudeman, C.S.; Begemann, M.H.; Pfaff, J.; Saykally, R.J., Velocity-Modulated Infrared Laser Spectroscopy of Molecular Ions: The ν_{1} Band of HCO^{+}, Phys. Rev. Lett., 1983, 50, 10, 727, https://doi.org/10.1103/PhysRevLett.50.727 . [all data]

Amano, 1983
Amano, T., The ν1 fundamental band of HCO+ by difference frequency laser spectroscopy, J. Chem. Phys., 1983, 79, 7, 3595, https://doi.org/10.1063/1.446216 . [all data]

Owrutsky, Keim, et al., 1989
Owrutsky, J.C.; Keim, E.R.; Coe, J.V.; Saykally, R.J., Absolute IR intensities of the .nu.1 bands of hydrodinitrogen(1+) and oxomethylium determined by direct laser absorption spectroscopy in fast ion beams, J. Phys. Chem., 1989, 93, 16, 5960, https://doi.org/10.1021/j100353a003 . [all data]

Keim, Polak, et al., 1990
Keim, E.R.; Polak, M.L.; Owrutsky, J.C.; Coe, J.V.; Saykally, R.J., Absolute infrared vibrational band intensities of molecular ions determined by direct laser absorption spectroscopy in fast ion beams, J. Chem. Phys., 1990, 93, 5, 3111, https://doi.org/10.1063/1.458845 . [all data]

Nizkorodov, Maier, et al., 1995
Nizkorodov, S.A.; Maier, J.P.; Bieske, E.J., The infrared spectrum of He--HCO+, J. Chem. Phys., 1995, 103, 4, 1297, https://doi.org/10.1063/1.469806 . [all data]

Nizkorodov, Dopfer, et al., 1996
Nizkorodov, S.A.; Dopfer, O.; Meuwly, M.; Maier, J.P.; Bieske, E.J., Mid-infrared spectra of the proton-bound complexes Nen--HCO+ (n=1,2), J. Chem. Phys., 1996, 105, 5, 1770, https://doi.org/10.1063/1.472052 . [all data]

Nizkorodov, Dopfer, et al., 1995
Nizkorodov, S.A.; Dopfer, O.; Ruchti, T.; Meuwly, M.; Maier, J.P.; Bieske, E.J., Size Effects in Cluster Infrared Spectra: the .nu.1 Band of Arn-HCO+ (n = 1-13), J. Phys. Chem., 1995, 99, 47, 17118, https://doi.org/10.1021/j100047a013 . [all data]

Bieske, Nizkorodov, et al., 1995
Bieske, E.J.; Nizkorodov, S.A.; Bennett, F.R.; Maier, J.P., The infrared spectrum of the H2--HCO+ complex, J. Chem. Phys., 1995, 102, 13, 5152, https://doi.org/10.1063/1.469240 . [all data]

Davies and Rothwell, 1984
Davies, P.B.; Rothwell, W.J., Diode laser detection of the bending mode of HCO+, J. Chem. Phys., 1984, 81, 12, 5239, https://doi.org/10.1063/1.447688 . [all data]

Kawaguchi, Yamada, et al., 1985
Kawaguchi, K.; Yamada, C.; Saito, S.; Hirota, E., Magnetic field modulated infrared laser spectroscopy of molecular ions: The ν2 band of HCO+, J. Chem. Phys., 1985, 82, 4, 1750, https://doi.org/10.1063/1.448407 . [all data]

Foltynowicz, Robinson, et al., 2000
Foltynowicz, R.J.; Robinson, J.D.; Zuckerman, E.J.; Hedderich, H.G.; Grant, E.R., Experimental Characterization of the Higher Vibrationally Excited States of HCO+: Determination of ω2, x22, g22, and B(030), J. Mol. Spectrosc., 2000, 199, 2, 147, https://doi.org/10.1006/jmsp.1999.8014 . [all data]

Foster, McKellar, et al., 1984
Foster, S.C.; McKellar, A.R.W.; Sears, T.J., Observation of the ν3 fundamental band of HCO+, J. Chem. Phys., 1984, 81, 1, 578, https://doi.org/10.1063/1.447344 . [all data]

Davies, Hamilton, et al., 1984
Davies, P.B.; Hamilton, P.A.; Rothwell, W.J., Infrared laser spectroscopy of the ν3 fundamental of HCO+, J. Chem. Phys., 1984, 81, 4, 1598, https://doi.org/10.1063/1.447889 . [all data]

Liu, Lee, et al., 1988
Liu, D.-J.; Lee, S.-T.; Oka, T., The ν3 fundamental band of HCNH+ and the 2ν3 ← ν3 and ν2 + ν3 ← ν2 hot bands of HCO+, J. Mol. Spectrosc., 1988, 128, 1, 236, https://doi.org/10.1016/0022-2852(88)90221-4 . [all data]

Linnartz, Speck, et al., 1998
Linnartz, H.; Speck, T.; Maier, J.P., High-resolution infrared spectrum of the ν3 band in Ar--HCO+, Chem. Phys. Lett., 1998, 288, 2-4, 504, https://doi.org/10.1016/S0009-2614(98)00304-2 . [all data]

Jacox, 1994
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules, American Chemical Society, Washington, DC, 1994, 464. [all data]

Jacox, 1998
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules: supplement A, J. Phys. Chem. Ref. Data, 1998, 27, 2, 115-393, https://doi.org/10.1063/1.556017 . [all data]

Jacox, 2003
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules: supplement B, J. Phys. Chem. Ref. Data, 2003, 32, 1, 1-441, https://doi.org/10.1063/1.1497629 . [all data]

Dyke, Jonathan, et al., 1980
Dyke, J.M.; Jonathan, N.B.H.; Morris, A.; Winter, M.J., The first ionization potential of the formyl radical, HCO(X2A'), studied using photoelectron spectroscopy, Mol. Phys., 1980, 39, 629. [all data]

Bogey, Demuynck, et al., 1981
Bogey, M.; Demuynck, C.; Destombes, J.L., Centrifugal distortion effects in HCO, Mol. Phys., 1981, 43, 5, 1043, https://doi.org/10.1080/00268978100101861 . [all data]

Sastry, Herbst, et al., 1981
Sastry, K.V.L.N.; Herbst, E.; De Lucia, F.C., Millimeter and submillimeter spectra of HCO+ and DCO+, J. Chem. Phys., 1981, 75, 8, 4169, https://doi.org/10.1063/1.442513 . [all data]

Woods, Saykally, et al., 1981
Woods, R.C.; Saykally, R.J.; Anderson, T.G.; Dixon, T.A.; Szanto, P.G., The molecular structure of HCO+ by the microwave substitution method, J. Chem. Phys., 1981, 75, 9, 4256, https://doi.org/10.1063/1.442627 . [all data]

Foster and McKellar, 1984
Foster, S.C.; McKellar, A.R.W., The ν3 fundamental bands of HN+2, DN+2, and DCO+, J. Chem. Phys., 1984, 81, 8, 3424, https://doi.org/10.1063/1.448066 . [all data]

Kawaguchi, McKellar, et al., 1986
Kawaguchi, K.; McKellar, A.R.W.; Hirota, E., Magnetic field modulated infrared laser spectroscopy of molecular ions: The ν1 band of DCO+, J. Chem. Phys., 1986, 84, 3, 1146, https://doi.org/10.1063/1.450503 . [all data]

Dyke, 1987
Dyke, J.M., J. Chem. Soc., 1987, Faraday Trans. 2 83, 69. [all data]

Woods, 1988
Woods, R.C., Microwave Spectroscopy of Molecular Ions in the Laboratory and in Space [and Discussion], Phil. Trans. Roy. Soc. (London) A324, 1988, 324, 1578, 141, https://doi.org/10.1098/rsta.1988.0007 . [all data]

Ohshima, Sumiyoshi, et al., 1997
Ohshima, Y.; Sumiyoshi, Y.; Endo, Y., Rotational spectrum of the Ar--HCO+ ionic complex, J. Chem. Phys., 1997, 106, 7, 2977, https://doi.org/10.1063/1.473416 . [all data]

Olkhov, Nizkorodov, et al., 1997
Olkhov, R.V.; Nizkorodov, S.A.; Dopfer, O., Hindered rotation in ion-neutral molecular complexes: The ν[sub 1] vibration of H[sub 2]--HCO[sup +] and D[sub 2]--DCO[sup +], J. Chem. Phys., 1997, 107, 20, 8229, https://doi.org/10.1063/1.475027 . [all data]

Foltynowicz, Robinson, et al., 2001
Foltynowicz, R.J.; Robinson, J.D.; Grant, E.R., Double-resonant photoionization efficiency spectroscopy: A precise determination of the adiabatic ionization potential of DCO, J. Chem. Phys., 2001, 114, 12, 5224, https://doi.org/10.1063/1.1349080 . [all data]

Foltynowicz, Robinson, et al., 2001, 2
Foltynowicz, R.J.; Robinson, J.D.; Grant, E.R., An experimental measure of anharmonicity in the bending of DCO[sup +], J. Chem. Phys., 2001, 115, 2, 878, https://doi.org/10.1063/1.1379336 . [all data]

Dore, Beninati, et al., 2003
Dore, L.; Beninati, S.; Puzzarini, C.; Cazzoli, G., Study of vibrational interactions in DCO[sup +] by millimeter-wave spectroscopy and determination of the equilibrium structure of the formyl ion, J. Chem. Phys., 2003, 118, 17, 7857, https://doi.org/10.1063/1.1564042 . [all data]


Notes

Go To: Top, Reaction thermochemistry data, Vibrational and/or electronic energy levels, References