nist_webbook_2026 ================= P\. J\. Linstrom and W\. G\. Mallard \(eds\.\), NIST Chemistry WebBook, NIST Standard Reference Database 69, National Institute of Standards and Technology, https\://webbook\.nist\.gov, gas\-phase ion energetics \(ionization energy determinations\), queried 2026\-09\-26, and constants of diatomic molecules \(K\. P\. Huber and G\. Herzberg\), queried 2026\-10\-07 `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.18434/T4D303 `__ **Source kind:** database **Recorded technique:** The WebBook's ion\-energetics pages list, for each molecule, the published determinations of the first ionisation energy \(eV\) with the method \(S spectroscopy, PE photoelectron, PI photoionisation, EI electron impact, EVAL evaluation\), the reference and a comment \('Vertical value' where the determination is vertical\)\. The compilations behind them are Lias et al\. \(J\. Phys\. Chem\. Ref\. Data 17, Suppl\. 1, 1988\) and its updates\. **Materials in structured entries:** CH4, CO, CO2, D2, H2, N2, N2O, O2, SF6 **Dataset quantities:** electronic\_state\_energy, ionization\_energy **Contents:** 33 datasets; 0 formulas. Curation notes -------------- A stopgap for the molecules' ionisation energies until the primary papers are in the library \(TC\-444; they are requested on the roadmap page\)\. Every value here is the WebBook's listing of one primary determination, recorded as reproduced from it, with the reference as the WebBook prints it\: one adiabatic determination per molecule \(the most precise spectroscopic or threshold value listed\) and, where listed, one vertical value\. The WebBook pages were read, not stored \(NIST Standard Reference Data\)\. The uncertainty level is not stated\. Page URLs\: https\://webbook\.nist\.gov/cgi/cbook\.cgi?ID=\&Mask=20 with CAS C1333740 \(H2\), C7782390 \(D2\), C7727379 \(N2\), C7782447 \(O2\), C74828 \(CH4\), C2551624 \(SF6\), C10024972 \(N2O\), C124389 \(CO2\)\. RE\-POINTED\: the primaries of eight datasets are now curated, and their reproduced\_from names the curated record\: adiabatic\_N2 \(trickl\_1989\), adiabatic\_O2 \(tonkyn\_1989\), adiabatic\_CH4 \(berkowitz\_1987\), vertical\_CH4 \(bieri\_1977, itself a reprint of Heilbronner, Jones & Maier 1977\), adiabatic\_SF6 \(frost\_1967\), vertical\_SF6 \(potts\_1970\), adiabatic\_N2O \(berkowitz\_1977\) and adiabatic\_CO2 \(wang\_1988\)\. No value was changed; each dataset's notes compare the WebBook's number with the paper's\. Still not curated\: McCormack et al\. 1989 \(H2; shiner\_1993 recombines its Rydberg measurement, and liu\_2010 quotes Liu et al\. 2009\), Takezawa & Tanaka 1975 \(D2; liu\_2010 reprints it with a \-1\.0 cm^\-1 correction\), Banna & Shirley 1976 \(O2 vertical\) and Potts & Williams 1974 \(N2O and CO2 vertical\)\. ELECTRONIC STATES \(queried 2026\-10\-07\)\. The WebBook's 'Constants of diatomic molecules' of H2, D2, N2, O2 and CO \(Mask=1000\), compiled by K\. P\. Huber and G\. H\. Herzberg \(data collected through February 1977\), are stored as returned, gzip\-compressed, in data/external/nist\_webbook/\\_diatomic\_constants\.html\.gz \(PROVENANCE\.md there, with the sha256 of each\)\. The datasets state\_\\_\ hold the Te of the states that bound where the third\-order response is off resonance\: the lowest dipole\-allowed, two\-photon\-allowed and spin\-forbidden excited states, with the 0\-0 band of the transition the page lists \(parameters\.nu00\_cm1, \.transition\) and the selection rules from the ground state \(\.one\_photon, \.two\_photon\: allowed, forbidden, spin\_forbidden; the curators' reading of the state's symmetry, TC\-863\)\. The strings are the page's, checked against the files by tests/test\_nist\_webbook\_states\.py; H&H's parentheses and brackets \(a doubtful or deduced value\) are stated in each dataset's notes\. Two Trans\. cells are garbled on the page\: D2's C state reads 'CX ↔' \(C ↔ X\) and its E state 'E → N', which is E → B\: with B's 0\-0 band it gives the EF\(0\)\-X\(0\) interval within 0\.4 cm^\-1 of liu\_2010's \(TC\-863\)\. Datasets -------- nist\_webbook\_2026/adiabatic\_H2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_H2", "material": "H2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "E. McCormack, J. M. Gilligan, C. Cornaggia and E. E. Eyler, Phys. Rev. A 39, 2260 (1989)" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 15\.425932 \+\- 0\.000002 eV, method S \(spectroscopy \(Rydberg series or threshold\)\), comment\: 'T = 0 K'\. Not re\-pointed \(the original is not in the library\)\. Against the curated values of the same \(N = 0 \-\> N\+ = 0\) interval\: shiner\_1993/mccormack\_H2 \(McCormack et al\.'s measurement with Shiner et al\.'s recalibration\) 124 417\.507\(12\) cm^\-1 = 15\.425805 eV, and liu\_2010/liu\_2009\_H2 124 417\.491 13\(37\) cm^\-1 = 15\.425803 eV \(hc = 1\.239841984e\-4 eV cm\)\. The WebBook's number is 0\.13 meV \(1\.0 cm^\-1\) higher, 60 times its stated uncertainty\. It is what a value near 124 417\.5 cm^\-1 gives with the old conversion 1 eV = 8065\.479 cm^\-1 \(124 417\.507 / 8065\.479 = 15\.425929 eV\), so the difference is the conversion factor, not the measurement \(an inference\: the WebBook states no factor\)\. nist\_webbook\_2026/adiabatic\_D2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_D2", "material": "D2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "S. Takezawa and Y. Tanaka, J. Mol. Spectrosc. 54, 379 (1975)" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 15\.4667 \+\- 0\.0001 eV, method S \(spectroscopy \(Rydberg series or threshold\)\)\. Not re\-pointed \(Takezawa & Tanaka 1975 is not in the library\)\. Against liu\_2010/ie\_ortho\_D2 \(X \(0, N = 0\) \-\> X\+ \(0, N\+ = 0\)\), 124 745\.394 07\(58\) cm^\-1 = 15\.466458 eV\: the WebBook's number is 0\.24 meV \(2\.0 cm^\-1\) higher\. liu\_2010's Table IV lists Takezawa & Tanaka's value as 124 745\.6\(6\) cm^\-1 with a \-1\.0 cm^\-1 pressure\-shift correction included \(liu\_2010/takezawa\_1975\_D2\), i\.e\. 124 746\.6 cm^\-1 as published; with 1 eV = 8065\.479 cm^\-1 that gives 15\.46673 eV, the WebBook's value to its last digit \(an inference\)\. So the WebBook's D2 value carries both the uncorrected pressure shift and the old conversion factor\. nist\_webbook\_2026/adiabatic\_N2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_N2", "material": "N2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "trickl_1989" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 15\.581 \+\- 0\.008 eV, method S \(spectroscopy \(Rydberg series or threshold\)\)\. The original, trickl\_1989/ie\_N2, is 125 666\.959\(67\) cm^\-1 = 15\.580717 eV \(hc = 1\.239841984e\-4 eV cm\) from X \(v = 0, J = 0\) to X\+ \(v\+ = 0, N\+ = 0\)\: the WebBook's rounding is 0\.28 meV high, within its \+\-0\.008 eV; the paper's uncertainty is 8\.3e\-6 eV\. nist\_webbook\_2026/adiabatic\_O2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_O2", "material": "O2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "tonkyn_1989" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 12\.0697 \+\- 0\.0002 eV, method S \(spectroscopy \(Rydberg series or threshold\)\)\. The original, tonkyn\_1989/ie\_O2, is 97348 \+\- 2 cm^\-1 = 12\.069614 eV \(\+\-0\.00025 eV\), from O2 X 3Sigma\_g\- F2 \(v = 0, J = 1\) to O2\+ X 2Pi\_\(1/2\)g \(v\+ = 0, J\+ = 1/2\)\: the WebBook's 12\.0697 is 0\.09 meV \(0\.7 cm^\-1\) above the conversion with the CODATA 2018 factor, within both uncertainties; with the old factor 1 eV = 8065\.479 cm^\-1, 97348 cm^\-1 gives 12\.06971 eV, the WebBook's value\. nist\_webbook\_2026/vertical\_O2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "vertical_O2", "material": "O2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "M. S. Banna and D. A. Shirley, J. Electron Spectrosc. Relat. Phenom. 8, 255 (1976)" ], "parameters": { "kind": "vertical", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 12\.33 \+\- 0\.01 eV, method PE \(photoelectron spectroscopy\), comment\: 'vertical value'\. nist\_webbook\_2026/adiabatic\_CH4 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_CH4", "material": "CH4", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "berkowitz_1987" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 12\.61 \+\- 0\.01 eV, method PI \(photoionisation mass spectrometry\)\. The original, berkowitz\_1987/adiabatic\_CH4, prints 12\.61 \(\+0\.01, \-0\.00\) eV \(983 \(\+0, \-1\) A\), the photoion\-yield onset at 78 K; the WebBook symmetrises the uncertainty\. By the paper's own rotational model the rotationless \(J = 0 \-\> 0\) value is about 0\.005 eV above the onset\. nist\_webbook\_2026/vertical\_CH4 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "vertical_CH4", "material": "CH4", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "bieri_1977" ], "parameters": { "kind": "vertical", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 13\.6 \+\- 0\.1 eV, method PE \(photoelectron spectroscopy\), comment\: 'vertical value'\. The paper it cites, bieri\_1977/vertical\_CH4, prints 13\.6 eV \(\+\-0\.1 eV\) as the first of three Jahn\-Teller maxima \(13\.6, 14\.4, 15\.0 eV\) of the 1t2 band, taken from Heilbronner, Jones & Maier, Helv\. Chim\. Acta 60, 1697 \(1977\) \(its reference \[17\]; curated as heilbronner\_1977, TC\-547\); the same value\. nist\_webbook\_2026/adiabatic\_SF6 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_SF6", "material": "SF6", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "frost_1967" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 15\.35 \+\- 0\.02 eV, method PE \(photoelectron spectroscopy\)\. The original, frost\_1967/first\_threshold\_SF6, prints 15\.35 eV \(standard deviation 0\.02 eV\), the first of four thresholds of the integrated retarding\-potential photoelectron curve; the paper does not call it adiabatic \(the WebBook's reading\)\. nist\_webbook\_2026/vertical\_SF6 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "vertical_SF6", "material": "SF6", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "potts_1970" ], "parameters": { "kind": "vertical", "final_state": "the cation's ground state" } } 1 inline points in the source record. As listed by the WebBook\: 15\.69 eV, method PE \(photoelectron spectroscopy\), comment\: 'vertical value'\. The original, potts\_1970/vertical\_SF6, prints 15\.69 eV \(t1u, the 3t1u band maximum; Table 8, p\. 75\), without uncertainty; the same value\. nist\_webbook\_2026/adiabatic\_N2O ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_N2O", "material": "N2O", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "berkowitz_1977" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 12\.886 \+\- 0\.002 eV, method PE \(photoelectron spectroscopy\)\. The original, berkowitz\_1977/adiabatic\_N2O, prints 12\.886 \+\- 0\.002 eV \(to X 2Pi\_3/2, the midpoint of the linear threshold rise, an approximation to the rotationless transition\); the same value\. The method is photoionisation mass spectrometry, not photoelectron spectroscopy as the WebBook lists it\. nist\_webbook\_2026/vertical\_N2O ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "vertical_N2O", "material": "N2O", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "potts_1974" ], "parameters": { "kind": "vertical", "final_state": "the cation's ground state" } } 1 inline points in the source record. As listed by the WebBook\: 12\.89 eV, method PE \(photoelectron spectroscopy\), comment\: 'vertical value'\. nist\_webbook\_2026/adiabatic\_CO2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "adiabatic_CO2", "material": "CO2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "wang_1988" ], "parameters": { "kind": "adiabatic", "final_state": "the cation's ground state" }, "uncertainty": { "column": true, "level": "not stated" } } 1 inline points in the source record. As listed by the WebBook\: 13\.778 \+\- 0\.002 eV, method PE \(photoelectron spectroscopy\)\. The original, wang\_1988/adiabatic\_CO2, prints 13\.778 eV \(Table 1, \+\-0\.002 eV; X 2Pi\_\(3/2\)g \(000\), 13\.7778 in Table 3\); the same value\. nist\_webbook\_2026/vertical\_CO2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "vertical_CO2", "material": "CO2", "quantity": "ionization_energy", "unit": "eV", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "potts_1974" ], "parameters": { "kind": "vertical", "final_state": "the cation's ground state" } } 1 inline points in the source record. As listed by the WebBook\: 13\.79 eV, method PE \(photoelectron spectroscopy\), comment\: 'vertical value'\. nist\_webbook\_2026/state\_H2\_B ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_H2_B", "material": "H2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "B 1Σu+ 2pσ", "kind": "Te", "one_photon": "allowed", "two_photon": "forbidden", "nu00_cm1": "90203.35", "transition": "B ↔ X 115 116 117 R" } } 1 inline points in the source record. H2 B 1Σu\+ 2pσ\: the lowest dipole\-allowed state\: the Lyman bands\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/H2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'B ↔ X 115 116 117 R'\. The 0\-0 band of that transition is at 90203\.35 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_H2\_C ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_H2_C", "material": "H2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "C 1Πu 2pπ", "kind": "Te", "one_photon": "allowed", "two_photon": "forbidden", "nu00_cm1": "99120.17", "transition": "C ↔ X 108 109 R" } } 1 inline points in the source record. H2 C 1Πu 2pπ\: the second dipole\-allowed state\: the Werner bands\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/H2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'C ↔ X 108 109 R'\. The 0\-0 band of that transition is at 99120\.17 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_H2\_E ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_H2_E", "material": "H2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "E 1Σg+ 2sσ", "kind": "Te", "one_photon": "forbidden", "two_photon": "allowed", "nu00_cm1": "8961.23", "transition": "E → B 102 V" } } 1 inline points in the source record. H2 E 1Σg\+ 2sσ\: the lowest state two photons reach \(the inner well of the EF double\-well state\)\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/H2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'E → B 102 V'\. The 0\-0 band of that transition is at 8961\.23 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_D2\_B ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_D2_B", "material": "D2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "B 1Σu+ 2pσ", "kind": "Te", "one_photon": "allowed", "two_photon": "forbidden", "nu00_cm1": "90633.79", "transition": "B ↔ X 64 65 R" } } 1 inline points in the source record. D2 B 1Σu\+ 2pσ\: the lowest dipole\-allowed state\: the Lyman bands\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/D2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'B ↔ X 64 65 R'\. The 0\-0 band of that transition is at 90633\.79 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_D2\_C ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_D2_C", "material": "D2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "C 1Πu 2pπ", "kind": "Te", "one_photon": "allowed", "two_photon": "forbidden", "nu00_cm1": "99409.18", "transition": "CX ↔ 59 R" } } 1 inline points in the source record. D2 C 1Πu 2pπ\: the second dipole\-allowed state\: the Werner bands\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/D2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'CX ↔ 59 R'\. The 0\-0 band of that transition is at 99409\.18 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_D2\_E ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_D2_E", "material": "D2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "E 1Σg+ 2sσ", "kind": "Te", "one_photon": "forbidden", "two_photon": "allowed", "nu00_cm1": "8827.99", "transition": "E → N V" } } 1 inline points in the source record. D2 E 1Σg\+ 2sσ\: the lowest state two photons reach \(the inner well of the EF double\-well state\)\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/D2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'E → N V'\. The 0\-0 band of that transition is at 8827\.99 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_N2\_A ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_N2_A", "material": "N2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "A 3Σu+", "kind": "Te", "one_photon": "spin_forbidden", "two_photon": "spin_forbidden", "nu00_cm1": "49754.78", "transition": "A↔X 108 104 R" } } 1 inline points in the source record. N2 A 3Σu\+\: the lowest excited state, a triplet\: the Vegard\-Kaplan bands\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/N2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'A↔X 108 104 R'\. The 0\-0 band of that transition is at 49754\.78 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_N2\_ap ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_N2_ap", "material": "N2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "a' 1Σu-", "kind": "Te", "one_photon": "forbidden", "two_photon": "forbidden", "nu00_cm1": "67739.31", "transition": "a' ↔ X 92 R" } } 1 inline points in the source record. N2 a' 1Σu\-\: the lowest excited singlet, reached from X only by forbidden one\-photon transitions \(Ogawa\-Tanaka\-Wilkinson\-Mulliken bands\)\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/N2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'a' ↔ X 92 R'\. The 0\-0 band of that transition is at 67739\.31 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_N2\_a ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_N2_a", "material": "N2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "a 1Πg", "kind": "Te", "one_photon": "forbidden", "two_photon": "allowed", "nu00_cm1": "1212.28", "transition": "a → a' 84 V" } } 1 inline points in the source record. N2 a 1Πg\: the lowest state two photons reach \(one\-photon only as the weak magnetic\-dipole and quadrupole Lyman\-Birge\-Hopfield bands\)\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/N2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'a → a' 84 V'\. The 0\-0 band of that transition is at 1212\.28 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_N2\_app ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_N2_app", "material": "N2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "a\" 1Σg+", "kind": "Te", "one_photon": "forbidden", "two_photon": "allowed", "nu00_cm1": "98840.30", "transition": "a\" ← X 64" } } 1 inline points in the source record. N2 a" 1Σg\+\: the second two\-photon state\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/N2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'a" ← X 64'\. The 0\-0 band of that transition is at 98840\.30 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. H&H print it as \[100016\.0\]\: parentheses and brackets mark a doubtful or deduced value \(the page's notes\)\. nist\_webbook\_2026/state\_N2\_b ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_N2_b", "material": "N2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "b 1Πu", "kind": "Te", "one_photon": "allowed", "two_photon": "forbidden", "nu00_cm1": "31865.7", "transition": "b → a R" } } 1 inline points in the source record. N2 b 1Πu\: the lowest dipole\-allowed state\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/N2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'b → a R'\. The 0\-0 band of that transition is at 31865\.7 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. H&H print it as \(101675\)\: parentheses and brackets mark a doubtful or deduced value \(the page's notes\)\. nist\_webbook\_2026/state\_O2\_a ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_O2_a", "material": "O2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "a 1Δg", "kind": "Te", "one_photon": "spin_forbidden", "two_photon": "spin_forbidden", "nu00_cm1": "7882.39", "transition": "a ↔ X 67 68 65 R" } } 1 inline points in the source record. O2 a 1Δg\: the lowest excited state, a singlet \(the 1\.27 um band, magnetic dipole\)\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/O2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'a ↔ X 67 68 65 R'\. The 0\-0 band of that transition is at 7882\.39 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_O2\_b ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_O2_b", "material": "O2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "b 1Σg+", "kind": "Te", "one_photon": "spin_forbidden", "two_photon": "spin_forbidden", "nu00_cm1": "5238.5", "transition": "b → a 63" } } 1 inline points in the source record. O2 b 1Σg\+\: a singlet \(the 762 nm atmospheric A band, magnetic dipole\)\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/O2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'b → a 63'\. The 0\-0 band of that transition is at 5238\.5 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_O2\_A ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_O2_A", "material": "O2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "A 3Σu+", "kind": "Te", "one_photon": "forbidden", "two_photon": "forbidden", "nu00_cm1": "21886", "transition": "(A → b) 50" } } 1 inline points in the source record. O2 A 3Σu\+\: the Herzberg I bands, forbidden as electric\-dipole transitions\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/O2\_diatomic\_constants\.html\.gz\); their Trans\. column reads '\(A → b\) 50'\. The 0\-0 band of that transition is at 21886 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_O2\_B ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_O2_B", "material": "O2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "B 3Σu-", "kind": "Te", "one_photon": "allowed", "two_photon": "forbidden", "nu00_cm1": "49358.15", "transition": "B ↔ X 46 47 R" } } 1 inline points in the source record. O2 B 3Σu\-\: the lowest dipole\-allowed state\: the Schumann\-Runge bands and continuum\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/O2\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'B ↔ X 46 47 R'\. The 0\-0 band of that transition is at 49358\.15 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_O2\_C ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_O2_C", "material": "O2", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "C (3Πg)", "kind": "Te", "one_photon": "forbidden", "two_photon": "allowed", "nu00_cm1": "65670", "transition": "(C ← X)" } } 1 inline points in the source record. O2 C \(3Πg\)\: the lowest triplet gerade state, which two photons reach\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/O2\_diatomic\_constants\.html\.gz\); their Trans\. column reads '\(C ← X\)'\. The 0\-0 band of that transition is at 65670 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. H&H print it as \(65530\)\: parentheses and brackets mark a doubtful or deduced value \(the page's notes\)\. nist\_webbook\_2026/state\_CO\_a ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_CO_a", "material": "CO", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "a 3Πr", "kind": "Te", "one_photon": "spin_forbidden", "two_photon": "spin_forbidden", "nu00_cm1": "48473.22", "transition": "a ↔ X 74 75 R" } } 1 inline points in the source record. CO a 3Πr\: the lowest excited state, a triplet\: the Cameron bands\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/CO\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'a ↔ X 74 75 R'\. The 0\-0 band of that transition is at 48473\.22 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_CO\_A ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_CO_A", "material": "CO", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "A 1Π", "kind": "Te", "one_photon": "allowed", "two_photon": "allowed", "nu00_cm1": "64748.48", "transition": "A ↔ X 50 51 52 R" } } 1 inline points in the source record. CO A 1Π\: the lowest dipole\-allowed state \(the fourth\-positive bands\); without an inversion centre it is also two\-photon allowed\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/CO\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'A ↔ X 50 51 52 R'\. The 0\-0 band of that transition is at 64748\.48 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_CO\_I ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_CO_I", "material": "CO", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "I 1Σ-", "kind": "Te", "one_photon": "forbidden", "two_photon": "forbidden", "nu00_cm1": "64546.26", "transition": "I ← X R" } } 1 inline points in the source record. CO I 1Σ\-\: reached by two photons only through the antisymmetric part of the two\-photon tensor \(Sigma\+ to Sigma\-\), which vanishes for degenerate or parallel photons\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/CO\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'I ← X R'\. The 0\-0 band of that transition is at 64546\.26 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. nist\_webbook\_2026/state\_CO\_D ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "state_CO_D", "material": "CO", "quantity": "electronic_state_energy", "unit": "cm-1", "abscissa": "label", "use": "reproduced", "reproduced_from": [ "K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constants of Diatomic Molecules (Van Nostrand Reinhold, New York, 1979), data collected through February 1977" ], "parameters": { "state": "D 1Δ", "kind": "Te", "one_photon": "forbidden", "two_photon": "allowed", "nu00_cm1": "65391", "transition": "D ← X R" } } 1 inline points in the source record. CO D 1Δ\: a two\-photon state just above A\. Te \(cm^\-1\), the minimum of the state's potential above that of X, as Huber & Herzberg tabulate it \(WebBook constants of diatomic molecules, data/external/nist\_webbook/CO\_diatomic\_constants\.html\.gz\); their Trans\. column reads 'D ← X R'\. The 0\-0 band of that transition is at 65391 cm^\-1 \(parameters\.nu00\_cm1, \.transition\); with the lower state's own 0\-0 band to X it gives T0, the energy from the ground level\. Formulas -------- No formulas are recorded. Corrections ----------- No dataset errata are recorded in this source record. Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register ` for the checks and decisions.