Internal Methyl Rotation in the CH Stretching Overtone Spectra of Toluene-α-<i>d</i><sub>2</sub>, -α-<i>d</i><sub>1</sub>, and -<i>d</i><sub>0</sub>
Bibliographic record
Abstract
The room-temperature vapor phase overtone spectrum of toluene-α- d 2 has been recorded in the CH stretching region corresponding to Δ v CH = 2−6 with conventional near-infrared spectroscopy (Δ v CH = 2−4) and with intracavity titanium:sapphire and dye laser photoacoustic spectroscopy (Δ v CH = 4−6). Both absolute oscillator strengths (conventional spectra) and relative oscillator strengths within a given overtone (conventional and photoacoustic spectra) have been measured. The aryl region of the spectrum is interpreted in terms of two nonequivalent aryl local modes and is essentially identical to the aryl regions of the spectra of toluene- d 0 and toluene-α- d 1 . However, the methyl band profile differs significantly in these three molecules. We use an anharmonic oscillator local mode model and an ab initio dipole moment function to calculate oscillator strengths for the aryl and methyl transitions. Parameters for this model come from a fit of the aryl transition energies and from a fit of the methyl spectral profiles. These simple calculations give values that are in good agreement with observed absolute and relative intensities. Differences in the methyl profiles in toluene- d 0, -α- d 1, and -α- d 2 are ascribed to coupling between CH stretching and methyl torsional modes. The methyl profiles are simulated on the basis of a simple adiabatic model that incorporates the harmonically coupled anharmonic oscillator local mode approach and our intensity calculations. The model successfully accounts for the change in methyl profiles between the three molecules, demonstrates the importance of torsional stretching coupling, and shows that coupling between the CH stretching oscillators is unimportant for higher overtones (Δ v CH ≥ 4).
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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) | 0.002 | 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".