Momentum-transfer dependence of Fano parameters for the (1s<sup>2</sup>)<sup>1</sup>S → (2s2p)<sup>1</sup>P doubly excited transition in helium
Bibliographic record
Abstract
We report the first detailed characterization of absolute generalized oscillator strength (GOS) of the (1s 2 ) 1 S→(2s2p) 1 P doubly excited transition in helium as a function of momentum transfer ( K ) by angle-resolved electron energy loss spectroscopy at 2.5 keV impact energy. The GOS profile is found to be dominated by a strong maximum at K = 0, characteristic of dipole-dominated interactions. Extrapolating our GOS profile to K = 0 using a semi-empirical power series (Lassettre series) gives an absolute OS of 0.0052, in good accord with theoretical and experimental optical values reported in the literature. Changes in the Fano parameters for the doubly excited transition are determined for the first time as a function of momentum transfer. The Fano profile index ( q ) increases rapidly from -2.75 in the K = 0 limit (observed earlier optically) to -1.5 at K 2 ~ 1.5 au and levels off to -1.0 at K 2 ~ 4 au, while the Fano correlation coefficient (ρ 2 ) decreases slowly from 0.04 at K ~ 0 to 0.03 at K 2 ~ 4 au. These variations reflect the intricate nature of the transition matrix elements involved in the interference between direct ionization and autoionization. Finally, we also obtain clear evidence for the presence of a non-dipole autoionizing resonance near 58.1 eV in He in the higher- K region, confirming an earlier theoretical prediction.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".