he_2021 ======= Q\. He, Z\. Fang, O\. Shoshanim, S\. S\. Brown and Y\. Rudich, Atmos\. Chem\. Phys\. 21, 14927 \(2021\) `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.5194/acp\-21\-14927\-2021 `__ **Source kind:** measurement **Recorded technique:** Broadband cavity\-enhanced spectroscopy \(two channels, 307\-350 and 338\-725 nm, 0\.8 nm resolution; 94\.0 \+\- 0\.1 cm cavity\), calibrated with He and N2 \(n\-based cross sections of Table 1\), plus cavity ring\-down spectroscopy at 404 and 662 nm\. Pure CO2, N2O, SF6; O2 \+ He and CH4 \+ He mixtures \(10\-100 %\)\. About 295 K and 1020 hPa\. **Materials in structured entries:** CH4, CO2, He, N2, N2O, O2, SF6 **Dataset quantities:** None recorded. **Contents:** 0 datasets; 11 formulas. Curation notes -------------- The measured quantity is the extinction \(Rayleigh scattering plus absorption\) cross section, related to the refractive index by Eq\. \(1\), sigma = 24 pi^3 nu^4 / N^2 \(\(n^2 \- 1\)/\(n^2 \+ 2\)\)^2 F\_k\(nu\)\. Overall 1\-sigma uncertainty 'within 1\.7 %' \(p\. 6\), mostly the N2 reference cross section \(1 %\); mean 1\.2\-1\.3 % \(CO2\), 1\.2\-1\.7 % \(N2O\), 1\.2\-1\.4 % \(SF6\) \(p\. 6\)\. The BBCES and CRDS results agree within 0\.9 % \(p\. 6\)\. Table 2 \(tbl\_7b887ae8ae76, JSON only, image checked\) gives the measured \('Exp'\) and n\-based cross sections \(10^\-27 cm^2\) of CO2, SF6, N2O, O2 and CH4 at 330, 404, 532, 660 and 710 nm\. They are NOT extracted\: the package has no quantity for a Rayleigh \(or extinction\) cross section, and converting them to refractive indices would be a transformation of printed values\. A 'rayleigh\_cross\_section' quantity \(with the King factor F\_k as a parameter\) is needed; the extraction is then direct\. For CH4 above about 400 nm and O2 in its bands the 'Exp' values include absorption \(pp\. 5, 9\)\. The refractive indices the paper derives from the cross sections are shown only in Fig\. 9\. Refractive indices \(and the formulas below\) refer to 288\.15 K and 1013\.25 hPa with N = 2\.546899e19 cm^\-3 \(an ideal\-gas density\), except O2's reproduced formula at 273\.15 K and 1013\.25 hPa with N = 2\.68678e19 cm^\-3 \(Table 1 footnote, read from the original PDF\: the library truncates it to '8678 x 1019 molec\. cm\-3'\)\. F\_k = 1 for SF6 and CH4\. Check of the reproduced Table 1 formulas\: with Eq\. \(1\) and the Table 1 F\_k they reproduce the n\-based column of Table 2 exactly for O2 and 0\.10\-0\.15 % high for CO2, SF6, N2O and CH4 at all five wavelengths \(a uniform offset, as if a density 0\.07 % higher had been used\), which confirms the transcription of the formulas \(checked 2026\-09\-24\)\. **Recorded bibliographic identity status:** VALIDATED. This concerns identification of the source; it does not establish the scientific correctness of its contents. Datasets -------- No datasets are recorded. Formulas -------- he\_2021/CH4\_uv ~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "CH4_uv", "material": "CH4", "equation": "Eq. (7), p. 10", "printed": "(n_CH4 - 1) x 10^8 = 5476 + 4.1579 x 10^14 / (1.1568 x 10^10 - nu^2)", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "fitted to this work's extinction data at 307-400 nm, where CH4 absorption is negligible", "coefficients": { "A": "5476", "B": "4.1579e14", "C": "1.1568e10" }, "check": "With F_k = 1 it gives 85.19, 36.09, 11.52, 4.773, 3.547 x 10^-27 cm^2 at 330, 404, 532, 660, 710 nm against the Exp column 85.3, 35.9, 11.3, 4.68, 3.47 (absorption above 400 nm is not in the formula) (checked 2026-09-24)." } Used by the paper to separate CH4 scattering from absorption; superseded by Eq\. \(10\) as the dispersion relation\. he\_2021/SF6 ~~~~~~~~~~~~ .. code-block:: text { "id": "SF6", "form": "dn_wavenumber2", "terms": { "scale": "1e-8", "A": "18997.7", "B": [ "8.27663e14" ], "C": [ "1.56833e10" ] }, "range_nm": [ 264.0, 725.0 ], "material": "SF6", "equation": "Eq. (8), p. 10", "printed": "(n_SF6 - 1) x 10^8 = 18997.7 + 8.27663 x 10^14 / (1.56833 x 10^10 - nu^2)", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "264-725 nm (this work's 307-725 nm data plus the data Wilmouth & Sayres 2020 fitted, equally weighted)", "coefficients": { "A": "18997.7", "B": "8.27663e14", "C": "1.56833e10" }, "check": "Gives 242.1, 104.5, 33.9, 14.14, 10.53 x 10^-27 cm^2 at the Table 2 wavelengths against Exp 239.4, 105.7, 34.1, 14.2, 10.4 (within 1.3 %) (checked 2026-09-24)." } Not independent of wilmouth\_2020's SF6 data, which it includes\. he\_2021/N2O ~~~~~~~~~~~~ .. code-block:: text { "id": "N2O", "form": "dn_wavenumber2", "terms": { "scale": "1e-8", "A": "22095", "B": [ "1.66291e14" ], "C": [ "6.75226e9" ] }, "range_nm": [ 307.0, 725.0 ], "material": "N2O", "equation": "Eq. (9), p. 10", "printed": "(n_N2O - 1) x 10^8 = 22095 + 1.66291 x 10^14 / (6.75226 x 10^9 - nu^2)", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "307-725 nm", "coefficients": { "A": "22095", "B": "1.66291e14", "C": "6.75226e9" }, "check": "With the Table 1 N2O King factor it gives 137.7, 57.25, 18.02, 7.417, 5.504 x 10^-27 cm^2 against Exp 136.7, 57.9, 18.3, 7.47, 5.48 (within 1.5 %) (checked 2026-09-24)." } Inverted from the measured cross sections with Sneep & Ubachs's F\_k \(Table 1\)\. he\_2021/CH4 ~~~~~~~~~~~~ .. code-block:: text { "id": "CH4", "form": "dn_wavenumber2", "terms": { "scale": "1e-8", "A": "3603.09", "B": [ "4.40362e14" ], "C": [ "1.1741e10" ] }, "range_nm": [ 264.0, 671.0 ], "material": "CH4", "equation": "Eq. (10), p. 11", "printed": "(n_CH4 - 1) x 10^8 = 3603.09 + 4.40362 x 10^14 / (1.1741 x 10^10 - nu^2)", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "264-671 nm (Wilmouth & Sayres 2019, 2020 at 264-297 and 333-363 nm, this work at 307-400 nm, Cuthbertson & Cuthbertson 1920 and Watson & Ramaswamy 1936 in the visible, all equally weighted)", "coefficients": { "A": "3603.09", "B": "4.40362e14", "C": "1.1741e10" }, "check": "Gives 84.33, 35.67, 11.37, 4.707, 3.497 x 10^-27 cm^2 against Exp 85.3, 35.9, 11.3, 4.68, 3.47 (checked 2026-09-24)." } Includes the Wilmouth & Sayres data and two visible refractometric data sets\: not independent of them\. he\_2021/He\_table1 ~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "He_table1", "form": "dn_wavenumber2", "terms": { "scale": "1e-8", "A": "2283", "B": [ "1.8102e13" ], "C": [ "1.5342e10" ] }, "range_nm": [ 300.0, 700.0 ], "material": "He", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 2283 + 1.8102 x 10^13 / (1.5342 x 10^10 - nu^2); F_k = 1.0", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "14285-33333 cm^-1 (300-700 nm)", "coefficients": { "A": "2283", "B": "1.8102e13", "C": "1.5342e10" }, "reproduced_from": [ "R. Abjean, A. Mehu and A. Johannin-Gilles, C. R. Acad. Sci. B 271, 835 (1970)", "leonard_1974", "cuthbertson_1932" ], "check": "Same as wilmouth_2020 He_table1." } Reproduced; the bold reference \(the formula's source\) is Leonard \(1974\)\. he\_2021/N2\_table1 ~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "N2_table1", "material": "N2", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 5677.465 + 318.81874 x 10^12 / (1.44 x 10^10 - nu^2); F_k = 1.034 + 3.17 x 10^-12 nu^2", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "21360-39370 cm^-1 (254-468 nm)", "coefficients": { "A": "5677.465", "B": "3.1881874e14", "C": "1.44e10" }, "reproduced_from": [ "D. R. Bates, Planet. Space Sci. 32, 785 (1984)", "M. Sneep and W. Ubachs, J. Quant. Spectrosc. Radiat. Transfer 92, 293 (2005)", "H. Naus and W. Ubachs, Opt. Lett. 25, 347 (2000)" ], "check": "Same coefficients as wilmouth_2020 N2_table1 (318.81874e12 = 3.1881874e14)." } Reproduced from Bates \(1984\), the UV branch of his formula\. he\_2021/CO2\_table1 ~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "CO2_table1", "material": "CO2", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 1.1427 x 10^11 x (5799.25/((128908.9)^2 - nu^2) + 120.05/((89223.8)^2 - nu^2) + 5.3334/((75037.5)^2 - nu^2) + 4.3244/((67837.7)^2 - nu^2) + 1.218145 x 10^-5/((2418.136)^2 - nu^2)); F_k = 1.1364 + 2.53 x 10^-11 nu^2", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "39417-55340 cm^-1 (181-254 nm) as listed; shown valid at 307-725 nm by the cross sections (p. 12)", "coefficients": { "scale": "1.1427e11", "B1": "5799.25", "C1": "128908.9", "B2": "120.05", "C2": "89223.8", "B3": "5.3334", "C3": "75037.5", "B4": "4.3244", "C4": "67837.7", "B5": "1.218145e-5", "C5": "2418.136" }, "reproduced_from": [ "A. Bideau-Mehu, Y. Guern, R. Abjean and A. Johannin-Gilles, Opt. Commun. 9, 432 (1973)", "G. R. Alms, A. K. Burnham and W. H. Flygare, J. Chem. Phys. 63, 3321 (1975)", "M. Sneep and W. Ubachs, J. Quant. Spectrosc. Radiat. Transfer 92, 293 (2005)" ], "check": "Reproduces Table 2's n-based CO2 column to 0.10-0.15 % (checked 2026-09-24); identical to wilmouth_2020 CO2_table1." } Refractive index from Bideau\-Mehu et al\. \(1973, bold\), King factor from Alms et al\. \(1975, italic\)\. he\_2021/CH4\_table1 ~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "CH4_table1", "material": "CH4", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 4869.8 + 4.1023 x 10^14 / (1.133 x 10^10 - nu^2); F_k = 1.0", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "15385-40000 cm^-1 (250-650 nm)", "coefficients": { "A": "4869.8", "B": "4.1023e14", "C": "1.133e10" }, "reproduced_from": [ "wilmouth_2020" ], "check": "Reproduces Table 2's n-based CH4 column to 0.15 % (checked 2026-09-24)." } Wilmouth & Sayres \(2020\) Eq\. \(7\)\. he\_2021/N2O\_table1 ~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "N2O_table1", "material": "N2O", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 46890 + 4.12 x 10^-6 nu^2; F_k = (3.3462 + 70.8 x 10^-12 nu^2)/(2.7692 - 47.2 x 10^-12 nu^2)", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "15453-21838 cm^-1 (458-647 nm, the five wavelengths of Alms et al.)", "coefficients": { "A": "46890", "B": "4.12e-6" }, "reproduced_from": [ "M. Sneep and W. Ubachs, J. Quant. Spectrosc. Radiat. Transfer 92, 293 (2005)", "G. R. Alms, A. K. Burnham and W. H. Flygare, J. Chem. Phys. 63, 3321 (1975)" ], "check": "Reproduces Table 2's n-based N2O column to 0.15 % (checked 2026-09-24)." } A Cauchy\-type \(polynomial in nu^2\) formula, from Alms et al\.'s polarizabilities at five visible wavelengths\. he\_2021/SF6\_table1 ~~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "SF6_table1", "material": "SF6", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 18611.4 + 8.9566 x 10^14 / (1.680 x 10^10 - nu^2); F_k = 1.0", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_15C", "density": "ideal", "range": "15385-40000 cm^-1 (250-650 nm)", "coefficients": { "A": "18611.4", "B": "8.9566e14", "C": "1.680e10" }, "reproduced_from": [ "wilmouth_2020" ], "check": "Reproduces Table 2's n-based SF6 column to 0.1 % (checked 2026-09-24)." } Wilmouth & Sayres \(2020\) Eq\. \(6\)\. he\_2021/O2\_table1 ~~~~~~~~~~~~~~~~~~~ .. code-block:: text { "id": "O2_table1", "material": "O2", "equation": "Table 1 (tbl_02a149a415f6), p. 3", "printed": "(n - 1) x 10^8 = 20564.8 + 2.480899 x 10^13 / (4.09 x 10^9 - nu^2); F_k = 1.09 + 1.385 x 10^-11 nu^2 + 1.448 x 10^-20 nu^4", "variable": "nu: vacuum wavenumber in cm^-1", "state": "1atm_0C", "density": "ideal", "range": "18315-34722 cm^-1 (288-546 nm)", "coefficients": { "A": "20564.8", "B": "2.480899e13", "C": "4.09e9" }, "reproduced_from": [ "D. R. Bates, Planet. Space Sci. 32, 785 (1984)", "U. Hohm, Mol. Phys. 78, 929 (1993)", "M. Sneep and W. Ubachs, J. Quant. Spectrosc. Radiat. Transfer 92, 293 (2005)" ], "check": "With N = 2.68678e19 cm^-3 it reproduces Table 2's n-based O2 column exactly (34.71, 14.57, 4.642, 1.924, 1.430) (checked 2026-09-24)." } At 273\.15 K and 1013\.25 hPa \(Table 1 asterisk\), unlike the other rows\. The paper's own O2 fit \(the generalised A \+ B/\(C \- nu^2\) form, p\. 5\) is not given numerically\. He et al\. cite Hohm, Mol\. Phys\. 78, 929 \(1993\) for it, which holds only hydrocarbons; Hohm's O2 dispersion is Mol\. Phys\. 81, 157 \(1994\), hohm\_1994b \(TC\-438\)\. 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.