au_1993#
J. W. Au, G. Cooper, G. R. Burton, T. N. Olney and C. E. Brion, “The valence shell photoabsorption of the linear alkanes, CnH2n+2 (n=1-8): absolute oscillator strengths (7-220 eV)”, Chem. Phys. 173, 209 (1993)
Source record · Catalogue · Review register
DOI: 10.1016/0301-0104(93)80142-v
Source kind: measurement
Recorded technique: Dipole (e,e) spectroscopy. Low resolution (1 eV FWHM, 8 keV, zero mean scattering angle): background-subtracted energy-loss spectra at 0.5, 1.0 and 2.0 eV intervals over 7-40, 40-80 and 80-220 eV, Bethe-Born converted; the valence-shell fraction above 220 eV from a fit of Eq. (1), df/dE = A E^-2 + B E^-3 + C E^-4, to 130-220 eV; the whole TRK-normalised to the number of valence electrons plus about 5 % for Pauli-excluded inner-shell transitions (8.33 for CH4). High resolution (0.048 eV FWHM, 3 keV): from the first threshold to at least 50 eV, normalised to the low resolution in the smooth continuum above about 20 eV (figures only). Matheson CH4, 99.8 % (pp. 2-4).
Materials in structured entries: CH4
Dataset quantities: differential_oscillator_strength, ionization_energy
Contents: 3 datasets; 1 formula.
Curation notes#
Values per molecule; no density or state involved (room-temperature gas, not stated). Only CH4 is curated. ‘The absolute oscillator strength scales are estimated to have an accuracy of +-5%’ (p. 3).
CH4 (datasets): Table 7 (p. 22), the low-resolution df/dE at 7.5-220 eV (176 points); the Eq. (1) tail fit with Table 2’s CH4 coefficients (formula tail_fit_CH4); Table 1’s quoted vertical ionisation potentials (13.6, 14.4, 15.0 eV for the Jahn-Teller split 1t2^-1 band, Kimura et al.’s HeI handbook; 22.91 eV for 2a1^-1, Potts and Streets 1974). Sums computed from Table 7 (2026-09-27; trapezoid plus the tail above 220 eV): S(0) = 7.915 over 7.5-220 eV and 8.330 in all (the normalisation 8.33); S(-1) = 10.533, S(-2) = 17.063 au, S(-3) = 31.45, S(-4) = 63.56, S(-5) = 137.9, S(-6) = 316.6. The paper prints no S(k). Olney et al. (1997, olney_1997) refine this spectrum for their CH4 dipole sums. Comparisons (pp. 4-6): good agreement with Okabe and Becker, Samson et al. and Backx et al. (1975; the last higher above 48 eV, attributed to its background subtraction); de Reilhac and Damany differ below 45 eV; Koch and Skibowski and Metzger and Cook differ in shape; the present data fall between Koch and Skibowski’s and Lee et al.’s synchrotron data at 21-24 eV. The recommended average DOSD values of Jhanwar, Meath and MacDonald (Can. J. Phys. 59, 185 (1981), not in the library) are compared in the figures only.
Table 3 (p. 7): the energies (experimental and calculated), term values and proposed Rydberg assignments of eight features of the high-resolution CH4 spectrum (1: 9.7 eV and 2: 10.5 eV, the Jahn-Teller split 1t2 -> 3s; 3-8 at 11.8-14.1 eV, 1t2 -> 4s, 3p, 3d, 4d), from Eq. (2) with R = 13.606 eV and quantum defects 1.13 (s), 0.6 (p), 0 (d): no quantity for a band position or term value; not extracted. Figs. 1-2 (CH4 low- and high-resolution spectra) are figures only.
THE OTHER ALKANES (not curated; not extracted): Table 1 also lists the vertical IPs of C2H6, C3H8 and C4H10; Table 2 the Eq. (1) coefficients of C2H6 ... C8H18 (5.4, 5.3, 4.4, 4.4, 4.4, 4.4, 5.1 % above 220 eV); Tables 4-6 the feature assignments of C2H6, C3H8, C4H10; Tables 8-14 the df/dE of C2H6 (7.5-220 eV), C3H8, C4H10, C5H12, C6H14, C7H16 and C8H18; TRK normalisations 14.54, 20.75, 26.96, 33.17, 39.38, 45.59, 51.80. Fig. 4 caption: the C2H6 1e_g -> 3s band (Gaussian fit centred at 8.7 eV) holds 2.15e-2; the C2H6 band at 8.7-10.1 eV about 0.26 (p. 10). Small peaks at 12.97 eV in the C2H6 and C4H10 spectra are N2 impurity (p. 4).
Recorded bibliographic identity status: VALIDATED_WITH_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.
Datasets#
au_1993/continuum#
{
"id": "continuum",
"material": "CH4",
"file": "CH4/au_1993__continuum.csv",
"table": "tbl_f5a4c303b9e9",
"quantity": "differential_oscillator_strength",
"unit": "1/eV",
"scale": 0.01,
"abscissa_unit": "eV",
"use": "primary",
"uncertainty": {
"relative": 0.05,
"level": "not stated"
}
}
Table 7 (unlabelled in the extraction): low-resolution (1 eV FWHM) dipole (e,e) absolute df/dE of CH4 (10^-2 eV^-1), 7.5-220 eV, 176 points in print order (0.5 eV steps to 40 eV, 1 eV to 80 eV, 2 eV to 220 eV); TRK-normalised to 8.33 with the Eq. (1) tail (formula tail_fit_CH4). Uncertainty +-5 % (p. 3).
au_1993/vertical_outer#
{
"id": "vertical_outer",
"material": "CH4",
"file": "CH4/au_1993__vertical_outer.csv",
"table": "tbl_8bb88b5f26fe",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"K. Kimura, S. Katsumata, Y. Achiba, T. Yamazaki and S. Iwata, Handbook of HeI Photoelectron Spectra of Fundamental Organic Molecules (Japan Scientific Society, Tokyo, 1981)"
],
"parameters": {
"kind": "vertical",
"final_state": "1t2^-1 (X 2T2), the Jahn-Teller components"
}
}
Table 1, CH4 outer valence: the vertical ionisation potentials of the 1t2 orbital, three values (13.6, 14.4, 15.0 eV) for the Jahn-Teller split band (the paper’s discussion, p. 6), rows 1t2_1-1t2_3, quoted from Kimura et al.’s handbook (Ref. [32]). The same three maxima as bieri_1977’s vertical_CH4 (Heilbronner et al.). No uncertainty printed.
au_1993/vertical_inner#
{
"id": "vertical_inner",
"material": "CH4",
"file": "CH4/au_1993__vertical_inner.csv",
"table": "tbl_8bb88b5f26fe",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"A. W. Potts and D. G. Streets, J. Chem. Soc. Faraday Trans. II 70, 875 (1974)"
],
"parameters": {
"kind": "vertical",
"final_state": "2a1^-1 (2A1)"
}
}
Table 1, CH4 inner valence: the vertical ionisation potential of the 2a1 orbital, 22.91 eV (row 2a1), quoted from Potts and Streets (Ref. [33]). bieri_1977 gives 22.9 eV. No uncertainty printed.
Formulas#
au_1993/tail_fit_CH4#
{
"id": "tail_fit_CH4",
"material": "CH4",
"equation": "Eq. (1), p. 4, with Table 2 (p. 4), CH4 row",
"printed": "df/dE = A E^-2 + B E^-3 + C E^-4; CH4: A (eV) = 1.4128x10^2, B (eV^2) = -2.8212x10^4, C (eV^3) = 2.0379x10^6, 5.0 % area above 220 eV",
"variable": "E: photon energy in eV; df/dE in eV^-1",
"state": "none (per molecule)",
"density": "none",
"range": "fitted over 130-220 eV; integrated from 220 eV to infinity for the valence-shell tail",
"coefficients": {
"A": "1.4128e2",
"B": "-2.8212e4",
"C": "2.0379e6"
},
"check": "The integral from 220 eV to infinity is 0.4145, 4.98 % of 8.33 (Table 2: 5.0 %); the curve gives 0.114e-2 /eV at 220 eV, 0.146e-2 at 180 eV and 0.265e-2 at 130 eV against Table 7's 0.12, 0.15 and 0.26 (computed 2026-09-27)."
}
The paper’s high-energy extrapolation of the CH4 low-resolution df/dE (Fig. 1a insert). Printed as mantissa x 10^n; stored in e-notation, digits unchanged. The other alkanes’ coefficients are in the source notes.
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.