Energetics of Br−H−Br<sup>-</sup> Formation from HBr Dimer Anion: An ab Initio Study
Bibliographic record
Abstract
Experimental studies have shown that the dissociative attachment of electrons to HBr monomer; viz., HBr + e - → H • + Br - is an endothermic process, which requires electrons of energy near the endothermicity (Δ E = +38 kJ/mol). In contrast the attachment to the dimer via the reaction: HBr·HBr + e - ⇌ HBr·HBr •- → H • + BrHBr - proceeds readily with electrons of thermal (i.e., near zero) energy. The energetics of the reactions with both the monomer and the dimer have been studied by ab initio methods. In each case the structure of the neutral and anion species have been computed using large basis sets and diffuse orbitals at the MP2 level. Energies have been obtained at this level and at the CCSD(T) level. The initial interaction of the free electron with the molecule produces a dipole continuum state (DCS) of the anion. The DCS subsequently undergoes a transition to a bound state via an avoided crossing. On the basis of the CCSD(T) energies, the H−Br • - ···HBr interaction lowers the energy for dissociation of the H−Br • - bond to the thermal energy range. Also the decomposition of HBr·HBr • - to H • and BrHBr - is 47 kJ/mol exergonic and the BrHBr - fragment is expected to be in a vibrationally excited state. In both the monomer and dimer anions the transition from DCS to the bound valence state is very sudden, and is marked by enormous (10-fold) changes in the dimensions of the orbitals occupied by the electron.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.008 | 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".