Stark Effect in the Benzene Dimer
Bibliographic record
Abstract
Ab initio calculations of the six-dimensional intermolecular potential have shown the benzene dimer to be an asymmetric top molecule at equilibrium with one benzene moiety forming the "stem" and the other a "tilted cap" in a T-shaped structure. Internal rotation of the cap about its C6 axis is essentially free; the barriers for cap tilting and for internal rotation of the stem about its C6 axis are hindered by successively higher barriers. In previous work we have validated these theoretical results using Fourier transform microwave spectroscopy in conjunction with dynamics calculations. We have also measured the Stark effect, and despite the fact that the equilibrium structure is that of an asymmetric top, the assigned transitions involving K = 0 exhibit a second-order Stark effect whereas those involving K = 1 exhibit a first-order Stark effect. This is typical for a symmetric-top molecule, but anomalous for an asymmetric-top molecule. We use symmetry arguments to explain how this asymmetric-top molecule can have a first-order Stark effect in certain states that have excitation of cap internal rotation. Cap internal rotation is essentially the twisting of the monomers relative to each other about the intermolecular axis, and such torsional motion occurs in other asymmetric top dimers such as benzene-CO and benzene-H2O. These latter dimers will also have levels that exhibit a first-order Stark effect, which we can explain using our symmetry arguments.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".