wilmouth_2019#
D. M. Wilmouth and D. S. Sayres, J. Quant. Spectrosc. Radiat. Transfer 234, 32 (2019)
Source record · Catalogue · Review register
DOI: 10.1016/j.jqsrt.2019.05.031
Source kind: measurement
Recorded technique: Broadband cavity-enhanced spectroscopy (BBCES), 333-363 nm: laser-driven Xe arc lamp (Energetiq EQ-99X-FC), 35 cm cavity of two plano-concave mirrors (peak reflectivity 0.998732 +- 0.000017 at 349.1 nm), 0.3 m Czerny-Turner spectrograph with CCD, calibrated on Hg lines. Pure gas filling the cavity, static, 1020-1060 hPa. Mirror reflectivity from N2 against He (Eq. 2, the n-based N2 cross section, +-1 %), then each sample’s extinction against He (Eq. 3). Purity 99.999 % (He, N2, Ar), 99.99 % (CO2, CH4), 99.8 % (SF6).
Materials in structured entries: Ar, CH4, CO2, SF6
Dataset quantities: rayleigh_cross_section
Contents: 4 datasets; 1 formula.
Curation notes#
The first of the authors’ two BBCES papers: this one covers 333-363 nm, wilmouth_2020 (JQSRT 255, 107224) 264-297 nm with the same apparatus and method. They are different papers and different data; wilmouth_2020’s Eqs. (5) and (7) for CH4 and (4) and (6) for SF6 are fitted to both papers’ data together, so they are not independent of this record’s Eq. (4) and of its ratios.
The measured cross sections are shown only in figures (Fig. 2b, 218 wavelengths over 333-363 nm per gas; Fig. 3, as 1-nm moving averages and as ratios to the n-based values; Fig. 4a, CH4’s n from them), never tabulated. The text prints (p. 37) the mean ratio of the measured to the n-based cross section over 333-363 nm, the n-based values from Table 1: Ar 0.998, CO2 0.990, SF6 0.978, CH4 0.778; and (p. 35) the mean 1-sigma uncertainty 2.5 % (Ar), 1.9 % (CO2), 1.6 % (SF6), 1.6 % (CH4): the root sum of squares of the run-to-run standard deviation, the effective path length (1.3 %, mostly the N2 reference cross section), temperature (0.3 %) and pressure (0.1 %). These are common to all four gases (one N2 reference) and to wilmouth_2020. The SF6 cross sections were raised by 0.1 % (and their uncertainty by 0.1 %) for the 99.8 % purity (air and CF4 impurities, p. 35). F_k = 1 for Ar, CH4 and SF6 (spherical, Bridge and Buckingham); CO2 F_k = 1.1364 + 2.53e-11 nu^2 (Table 1).
Table 1 (tbl_309d15b8e0de, image checked) gives the n-based formulas at N = 2.5469e19 cm^-3 (288.15 K, 101325 Pa, ideal): He, N2 (Bates’s UV branch, F_k 1.034 + 3.17e-12 nu^2), Ar (Peck & Fisher), CO2 (Bideau-Mehu with Alms’s F_k, the corrected 10^3 scale of Sneep & Ubachs’s Eq. 13), CH4 46662 + 4.02e-6 nu^2 and SF6 71517 + 4.996e-6 nu^2 (Sneep & Ubachs’s Eqs. 18 and 21). Identical to wilmouth_2020’s Table 1, where they are recorded as reproduced formulas; not repeated here. The authors correct ‘typographical errors in several papers in the literature’ in them (p. 33) without naming them.
RECONSTRUCTED, NOT PRINTED: the datasets below are band-centre cross sections at 348.0 nm, each the printed mean ratio times the n-based cross section of Table 1 at 348.0 nm (nu = 28735.6 cm^-1), computed here (2026-09-29): n-based Ar 2.6300e-26, CO2 7.8390e-26 (F_k 1.1573), SF6 1.9887e-25, CH4 8.6833e-26 cm^2. They assume the ratio is flat across the 30 nm band; for CH4 the ratio of Eq. (4)’s cross section to the n-based one runs 0.781-0.775 over 333-363 nm (mean 0.778, as printed), so the centre value stands for the band to 0.4 %; Eq. (4) itself gives 6.7552e-26 at 348.0 nm against the reconstruction’s 6.7556e-26. They are checks (validators), never fitted (TC-712).
Recorded bibliographic identity status: VALIDATED. This concerns identification of the source; it does not establish the scientific correctness of its contents.
Datasets#
wilmouth_2019/band_Ar#
{
"id": "band_Ar",
"material": "Ar",
"table": "text",
"quantity": "rayleigh_cross_section",
"unit": "cm2",
"scale": 1e-26,
"abscissa_unit": "nm",
"wavelength_medium": "vacuum",
"use": "check",
"uncertainty": {
"relative": 0.025,
"level": "1 sigma"
},
"parameters": {
"king_factor": 1.0
}
}
1 inline points in the source record.
Reconstructed, not printed (see the record’s notes): mean ratio 0.998 (p. 37) times the n-based 2.6300e-26 cm^2 of Table 1 (Peck & Fisher) at 348.0 nm; mean 1-sigma 2.5 % (p. 35). king_factor 1 (Table 1).
wilmouth_2019/band_CO2#
{
"id": "band_CO2",
"material": "CO2",
"table": "text",
"quantity": "rayleigh_cross_section",
"unit": "cm2",
"scale": 1e-26,
"abscissa_unit": "nm",
"wavelength_medium": "vacuum",
"use": "check",
"uncertainty": {
"relative": 0.019,
"level": "1 sigma"
},
"parameters": {
"king_factor": 1.1573
}
}
1 inline points in the source record.
Reconstructed, not printed: mean ratio 0.990 (p. 37) times the n-based 7.8390e-26 cm^2 of Table 1 (Bideau-Mehu’s formula, extrapolated from 181-254 nm, with Alms’s F_k) at 348.0 nm; mean 1-sigma 1.9 % (p. 35). king_factor: Table 1’s F_k = 1.1364 + 2.53e-11 nu^2 at 28735.6 cm^-1 (1.157291).
wilmouth_2019/band_SF6#
{
"id": "band_SF6",
"material": "SF6",
"table": "text",
"quantity": "rayleigh_cross_section",
"unit": "cm2",
"scale": 1e-26,
"abscissa_unit": "nm",
"wavelength_medium": "vacuum",
"use": "check",
"uncertainty": {
"relative": 0.016,
"level": "1 sigma"
},
"parameters": {
"king_factor": 1.0
}
}
1 inline points in the source record.
Reconstructed, not printed: mean ratio 0.978 (p. 37) times the n-based 1.9887e-25 cm^2 of Table 1 (Sneep & Ubachs’s Eq. 21, from Vukovic’s 633 and 1300 nm values) at 348.0 nm; mean 1-sigma 1.6 % (p. 35), including the 0.1 % purity term. king_factor 1.
wilmouth_2019/band_CH4#
{
"id": "band_CH4",
"material": "CH4",
"table": "text",
"quantity": "rayleigh_cross_section",
"unit": "cm2",
"scale": 1e-26,
"abscissa_unit": "nm",
"wavelength_medium": "vacuum",
"use": "check",
"uncertainty": {
"relative": 0.016,
"level": "1 sigma"
},
"parameters": {
"king_factor": 1.0
}
}
1 inline points in the source record.
Reconstructed, not printed: mean ratio 0.778 (p. 37) times the n-based 8.6833e-26 cm^2 of Table 1 (Sneep & Ubachs’s Eq. 18, from Hohm’s polarizabilities) at 348.0 nm; mean 1-sigma 1.6 % (p. 35). Eq. (4) gives 6.7552e-26 here. Reproducible over different days and with a second cylinder from another supplier (p. 37). king_factor 1 (assumed, Bridge and Buckingham, p. 37).
Formulas#
wilmouth_2019/CH4_eq4#
{
"id": "CH4_eq4",
"material": "CH4",
"equation": "Eq. (4), p. 37",
"printed": "(n - 1) x 10^8 = 40161.8 + 4.75 x 10^-6 nu^2",
"variable": "nu: vacuum wavenumber in cm^-1",
"state": "1atm_15C",
"density": "ideal",
"range": "333-363 nm (the data; 'increasing uncertainties' outside, p. 37)",
"coefficients": {
"A": "40161.8",
"B": "4.75e-6"
},
"check": "Through Eq. (1) (N = 2.5469e19 cm^-3, F_k = 1) its cross sections are 0.7780 of Table 1's CH4 n-based ones on average over 333-363 nm (0.781-0.775): the printed mean ratio 0.778 (p. 37). Against wilmouth_2020's Eq. (5) (UV only) the cross sections differ by -0.6 to +0.4 %, against its Eq. (7) by -1.1 to -0.4 % (computed 2026-09-29). Equation image eq_44add8785b39 checked."
}
The authors’ fit, A + B nu^2 by non-linear least squares (R^2 = 0.993), to n from their CH4 cross sections, Eq. (1) solved for n with F_k = 1, ‘scaled to 288.15 K and 101,325 Pa’ (p. 37): an ideal-gas density (N = 2.5469e19 cm^-3, Table 1 note a). A scattering-derived n, not a refractive-index measurement. Superseded for 250-650 nm by wilmouth_2020’s Eq. (7), which includes these data. ‘We recommend using the dispersion relation derived in this work (Eq. (4)) for CH4 in the UV-A spectral region’ (p. 39); uncertainty about 1.6 % in cross section.
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 review register for the checks and decisions.