Trifluoroacetic Acid and Trifluoroacetic Anhydride Radical Cations Dissociate near the Ionization Limit
Bibliographic record
Abstract
The threshold photoelectron spectra (TPES) and ion dissociation breakdown curves for trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAN) were measured by imaging photoelectron photoion coincidence spectroscopy employing both effusive room-temperature samples and samples introduced in a seeded molecular beam. The fine structure in the breakdown diagram of TFA mirroring the vibrational progression in the TPES suggests that direct ionization to the X̃ + state leads to parent ions with a lower “effective temperature” than nonresonant ionization in between the vibrational progression. Composite W1U, CBS-QB3, CBS-APNO, G3, and G4 calculations yielded an average ionization energy (IE) of 11.69 ± 0.06 eV, consistent with the experimental value of 11.64 ± 0.01 eV, based on Franck–Condon modeling of the TPES. The measured 0 K appearance energies (AE 0K ) for the reaction forming CO 2 H + + CF 3 from TFA were 11.92 for effusive data and 11.94 ± 0.01 eV for molecular beam data, consistent with the calculated composite method 0 K reaction energy of 11.95 ± 0.08 eV. Together with the 0 K heats of formation (Δ f H 0K ) of CO 2 H + and CF 3, this yields a Δ f H 0K of neutral TFA of −1016.6 ± 1.5 kJ mol –1 (−1028.3 ± 1.5 kJ mol –1 at 298 K). TFAN did not exhibit a molecular ion at room-temperature conditions, but a small signal was observed when rovibrationally cold species were probed in a molecular beam. The two observed dissociation channels were CF 3 C(O)OC(O) + + CF 3 and the dominant, sequential reaction CF 3 CO + + CF 3 + CO 2 . Calculations revealed a low-energy isomer of ionized TFAN, incorporating the three moieties CF 3 CO +, CF 3, and CO 2 joined in a noncovalent complex, mediating its unimolecular dissociation.
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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 | 0.000 |
| 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) | 0.003 | 0.001 |
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".