potts_1974#
A. W. Potts and T. A. Williams, “The observation of ‘forbidden’ transitions in He II photoelectron spectra”, J. Electron Spectrosc. Relat. Phenom. 3, 3 (1974)
Source record · Catalogue · Review register
DOI: 10.1016/0368-2048(74)80070-8
Source kind: measurement
Recorded technique: He II (30.4 nm, 40.8 eV) photoelectron spectroscopy with a d.c. discharge lamp; two spectrometers of 10 cm mean radius, a 127 degree cylindrical electrostatic analyser (with polystyrene filters to extend the energy range: the ‘filtered’ spectra, of ‘considerably lower resolution’ above 30 eV) and a 150 degree spherical analyser for the higher-resolution work (p. 6). The bands below the He I line (the ‘584 region’) are not measured here: they are taken from Turner, Baker, Baker & Brundle’s He I compilation (p. 7). The calibration and the accuracy are not stated.
Materials in structured entries: CO, CO2, N2, N2O
Dataset quantities: ionization_energy
Contents: 8 datasets; 0 formulas.
Curation notes#
PDF pages 1-15 = journal pages 3-17 (pages cited are journal pages). Identity checked on the first page: this is the paper requested for the vertical ionisation energies of N2O and CO2 (Potts & Williams, J. Electron Spectrosc. 3, 3 (1974)), the paper the NIST WebBook cites for them (nist_webbook_2026/vertical_N2O, 12.89 eV, and vertical_CO2, 13.79 eV).
WHAT THE ‘FORBIDDEN’ TRANSITIONS ARE (pp. 3-6, abstract): ‘anomalous bands’ in the He II spectra, ‘attributed to excitation of a second electron along with the primary ionization’, made possible by configuration interaction (CI) between ionised states of the same symmetry: two-electron (ionisation plus excitation) transitions to ‘superexcited ionized states’, which are forbidden in the one-electron picture and borrow intensity from an allowed ionisation to a state of the same symmetry; the UV analogue of the X-ray ‘shake-up’ satellites. The authors call them ‘CI bands’. They are observed for N2, CO, HCN, CO2, COS, CS2 and N2O (and in the He II spectra of O2, C2N2, SO2 and CH3I, p. 16, without values). The anomalous structure is not pressure dependent (so not electron energy loss) and, for N2, CO and HCN, lies below the energy at which autoionisation could cause it (p. 6).
WHAT THE TABLES HOLD: Tables 1 (p. 7) and 3 (p. 14): ‘In Tables 1 and 3, IP’s are band maxima or vertical IP’s. Those in the 584 region have been taken from Turner et al.[17]’ (p. 7; [17] = D. W. Turner, A. D. Baker, C. Baker and C. R. Brundle, Molecular Photoelectron Spectroscopy, Wiley-Interscience, London, 1970). So every value is a vertical ionisation energy (a band maximum), and those below the He I photon energy (21.22 eV) are Turner et al.’s, reprinted. The paper prints no adiabatic ionisation energy and no uncertainty.
EXTRACTED (tbl_5eb7440f6f19 and tbl_278510f78d78, JSON cells, images checked), ionization_energy, kind vertical, eV, one row per band labelled by the printed assignment (the valence-shell orbital numbering of the paper: N2’s 2sigma_g is the HOMO, 3sigma_g in all-electron numbering; CO’s 3sigma is 5sigma; CO2’s 1pi_g and N2O’s 2pi are the HOMOs), split at the He I line: - hei_<gas> (reproduced from Turner et al. 1970 by the caption note): N2 15.58 (2sigma_g), 16.98 (1pi_u), 18.75 (1sigma_u); CO 14.01, 16.91, 19.69; CO2 13.79 (1pi_g), 17.59, 18.08, 19.40; N2O 12.89 (2pi), 16.39, 18.24, 19.5 (CI), 20.11. N2O’s 19.5 eV CI band lies in the 584 region, so by the note it is Turner et al.’s too (an inference from the note; the text, p. 15, says theory assigns it and the 22.6 and 24.1 eV bands to 2Pi states of the configuration ...(2pi)^2(3pi)^1, Lorquet & Cadet [3]). - heii_<gas> (this paper’s He II measurements): N2 25.3 (CI; the C 2Sigma_u+ state), 28.8, 32.8 (CI), 36.6 (1sigma_g); CO 22.7, 23.4, 25.3, 28.1, 31.8 (CI), 37.3 (1sigma); CO2 22.6, 27.2, 31.4, 35.3 (CI), 38.5 (1sigma_g + 1sigma_u); N2O 22.6, 24.1, 28.7 (CI), 33.7 (2sigma), 37.3 (1sigma). Positions above 30 eV come from the filtered spectra, of ‘considerably lower resolution’ (Figs. 1 and 3 captions). The printed column of each file keeps the band’s four cells: the energy, the relative intensity, the assignment and the XPS energy.
BEARING: the first vertical energies, CO2 13.79 eV (to X 2Pi_g) and N2O 12.89 eV (to X 2Pi), are the values nist_webbook_2026 lists and attributes to this paper; they are Turner et al.’s 1970 He I values as this paper reprints them. Against the adiabatic energies curated: CO2 13.778(2) (wang_1988), 0.012 eV below; N2O 12.886(2) (berkowitz_1977), 0.004 eV below. N2’s 15.58 eV is the X 2Sigma_g+ band maximum (vertical); CO’s 14.01 eV likewise.
NOT EXTRACTED (notes only): - The relative band intensities (Tables 1 and 3; the first band = 1): no quantity. N2 1, 1.53, 0.40, 0.03, 0.10, 0.02, 0.07; CO 1, 3.1, 1.26, 0.01, 0.03, 0.02, 0.05, 0.21, 0.17; CO2 1, 0.48, 0.40, 0.26, 0.02, 0.09, 0.08, 0.08, 0.24; N2O 1, 0.31, 0.32, 0.04, 0.24, 0.02, 0.06, 0.03, 0.03, 0.07 (in the order of the bands above). - The XPS ionisation energies (Tables 1 and 3, the last row of each block): other authors’ X-ray values (N2 and CO from Siegbahn et al., ESCA Applied to Free Molecules (1969) [4] and ref. 19; CO2 from Allan et al. 1972/73 [14]; N2O from Connolly et al., J. Chem. Phys. 58, 4265 (1973) [23]), kept in the printed column only. - Table 1 footnotes: N2’s 25.3 eV band, ‘First level observed at 23.82 eV corresponding to V’ = 1, Delta G_1/2 ~ 2076 cm^-1’ (the C 2Sigma_u+ state’s progression); CO’s 22.7, 23.4 and 25.3 eV bands have Delta G_1/2 ~ 1480, 1690 and 1610 cm^-1 (ref. 18, Codling & Potts, in press). - Tables 2 and 4 (pp. 12, 15): the empirical assignments of the CI bands (predicted energies = IP + excitation energy of the neutral, Siegbahn’s approximation; excitation energies T0 from Herzberg and Mulliken). The calculated energies of Okuda & Jonathan (p. 10: 18.92 eV for N2’s (1pi_u)^-1, 21.10 eV for (1sigma_u)^-1, against the observed 16.98 and 18.75) are quoted in the text. - HCN (Table 1c), COS (3b) and CS2 (3c): not curated species. (Table 3c’s image has an eleventh CS2 band, 23.96 eV, CI, XPS 23.5, that the library’s cells lost; not taken.) - The valence configuration of N2O is printed ‘(1sigma)^2 (2sigma)^2 (3sigma)^2 (1pi)^2 (4sigma)^4 (2pi)^4’ (p. 14), with the 1pi and 4sigma occupancies interchanged (it should be (1pi)^4 (4sigma)^2 for 22 valence electrons; a misprint in the text, no value affected). - Figs. 1-3: the spectra, not digitised.
Recorded bibliographic identity status: VALIDATED_WITH_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents.
Datasets#
potts_1974/hei_N2#
{
"id": "hei_N2",
"material": "N2",
"file": "N2/potts_1974__hei_N2.csv",
"table": "tbl_5eb7440f6f19",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"D. W. Turner, A. D. Baker, C. Baker and C. R. Brundle, Molecular Photoelectron Spectroscopy, Wiley-Interscience, London, 1970"
],
"parameters": {
"kind": "vertical",
"final_state": "the row's one-hole state: X 2Sigma_g+ (2sigma_g^-1), A 2Pi_u, B 2Sigma_u+"
}
}
Table 1a, p. 7: the bands in the He I (584 A) region, ‘taken from Turner et al.’ (caption note); band maxima or vertical energies. Row = the ionised orbital (the paper’s valence numbering: 2sigma_g -> X 2Sigma_g+, 1pi_u -> A 2Pi_u, 1sigma_u -> B 2Sigma_u+). No uncertainty printed.
potts_1974/heii_N2#
{
"id": "heii_N2",
"material": "N2",
"file": "N2/potts_1974__heii_N2.csv",
"table": "tbl_5eb7440f6f19",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "primary",
"parameters": {
"kind": "vertical",
"final_state": "the row's ionisation: CI rows are two-electron (ionisation plus excitation) states of N2+; 1sigma_g the inner-valence hole"
}
}
Table 1a, p. 7: the He II bands above 21.22 eV, this paper’s. CI_25.3 is the C 2Sigma_u+ state (first level observed at 23.82 eV, v’ = 1; footnote a); CI_28.8 and CI_32.8 are two-electron satellites (record notes); 1sigma_g (36.6 eV) the inner-valence one-hole band, from the filtered, lower-resolution spectrum. No uncertainty printed.
potts_1974/hei_CO#
{
"id": "hei_CO",
"material": "CO",
"file": "CO/potts_1974__hei_CO.csv",
"table": "tbl_5eb7440f6f19",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"D. W. Turner, A. D. Baker, C. Baker and C. R. Brundle, Molecular Photoelectron Spectroscopy, Wiley-Interscience, London, 1970"
],
"parameters": {
"kind": "vertical",
"final_state": "the row's one-hole state: X 2Sigma+ (3sigma^-1), A 2Pi, B 2Sigma+"
}
}
Table 1b, p. 7: the He I region bands, ‘taken from Turner et al.’; band maxima or vertical energies. 3sigma -> X 2Sigma+, 1pi -> A 2Pi, 2sigma -> B 2Sigma+ (valence numbering). No uncertainty printed.
potts_1974/heii_CO#
{
"id": "heii_CO",
"material": "CO",
"file": "CO/potts_1974__heii_CO.csv",
"table": "tbl_5eb7440f6f19",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "primary",
"parameters": {
"kind": "vertical",
"final_state": "the row's ionisation: CI rows are two-electron states of CO+; 1sigma the inner-valence hole"
}
}
Table 1b, p. 7: the He II bands above 21.22 eV, this paper’s: five CI (two-electron) bands and the 1sigma inner-valence band (37.3 eV). The 22.7, 23.4 and 25.3 eV bands show vibrational structure (Fig. 2; footnotes b-d). No uncertainty printed.
potts_1974/hei_CO2#
{
"id": "hei_CO2",
"material": "CO2",
"file": "CO2/potts_1974__hei_CO2.csv",
"table": "tbl_278510f78d78",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"D. W. Turner, A. D. Baker, C. Baker and C. R. Brundle, Molecular Photoelectron Spectroscopy, Wiley-Interscience, London, 1970"
],
"parameters": {
"kind": "vertical",
"final_state": "the row's one-hole state: X 2Pi_g (1pi_g^-1), A 2Pi_u, B 2Sigma_u+, C 2Sigma_g+"
}
}
Table 3a, p. 14: the He I region bands, ‘taken from Turner et al.’ (the note under Table 1, which applies to Tables 1 and 3); band maxima or vertical energies. 1pi_g (13.79 eV) -> X 2Pi_g, the first vertical ionisation energy of CO2, the value the NIST WebBook lists from this paper; 1pi_u -> A 2Pi_u, 2sigma_u -> B 2Sigma_u+, 2sigma_g -> C 2Sigma_g+. No uncertainty printed.
potts_1974/heii_CO2#
{
"id": "heii_CO2",
"material": "CO2",
"file": "CO2/potts_1974__heii_CO2.csv",
"table": "tbl_278510f78d78",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "primary",
"parameters": {
"kind": "vertical",
"final_state": "the row's ionisation: CI rows are two-electron states of CO2+; 1sigma_g+1sigma_u the inner-valence holes"
}
}
Table 3a, p. 14: the He II bands above 21.22 eV, this paper’s: four CI bands and 1sigma_g + 1sigma_u (38.5 eV, unresolved inner-valence holes), the latter from the filtered spectrum. No uncertainty printed.
potts_1974/hei_N2O#
{
"id": "hei_N2O",
"material": "N2O",
"file": "N2O/potts_1974__hei_N2O.csv",
"table": "tbl_278510f78d78",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "reproduced",
"reproduced_from": [
"D. W. Turner, A. D. Baker, C. Baker and C. R. Brundle, Molecular Photoelectron Spectroscopy, Wiley-Interscience, London, 1970"
],
"parameters": {
"kind": "vertical",
"final_state": "the row's state: X 2Pi (2pi^-1), A 2Sigma+, B 2Pi, C 2Sigma+; CI_19.5 a two-electron state"
}
}
Table 3d, p. 14: the He I region bands, ‘taken from Turner et al.’; band maxima or vertical energies. 2pi (12.89 eV) -> X 2Pi, the first vertical ionisation energy of N2O, the value the NIST WebBook lists from this paper; 4sigma -> A 2Sigma+, 1pi -> B 2Pi, 3sigma -> C 2Sigma+; CI_19.5 a two-electron band (attributed to Turner et al. by the note’s rule: record notes). No uncertainty printed.
potts_1974/heii_N2O#
{
"id": "heii_N2O",
"material": "N2O",
"file": "N2O/potts_1974__heii_N2O.csv",
"table": "tbl_278510f78d78",
"quantity": "ionization_energy",
"unit": "eV",
"abscissa": "label",
"use": "primary",
"parameters": {
"kind": "vertical",
"final_state": "the row's ionisation: CI rows are two-electron states of N2O+; 2sigma, 1sigma the inner-valence holes"
}
}
Table 3d, p. 14: the He II bands above 21.22 eV, this paper’s: three CI bands and the 2sigma (33.7 eV) and 1sigma (37.3 eV) inner-valence bands, from the filtered spectrum. No uncertainty printed.
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 review register for the checks and decisions.