FTIR SYNCHROTRON SPECTROSCOPY OF THE LOWER MODES OF METHYL-D3 MERCAPTAN (CD3SH) – WHERE IS THE C-S STRETCH?
Bibliographic record
Abstract
The infrared Fourier transform spectrum of the lower vibrational modes of CD$_{3}$SH has been recorded in the 400-1200 cm$^{-1}$ region using synchrotron radiation at the FIR beamline of the Canadian Light Source in Saskatoon. Torsion-rotation assignments have been made for a relatively strong parallel band centered at 644 cm$^{-1}$ and a weaker perpendicular band centered at 727 cm$^{-1}$. Comparison with the spectra for the normal CH$_{3}$SH species as well as the analogous CD$_{3}$OH and CH$_{3}$OH methanol molecules would suggest an obvious association of the 644 cm$^{-1}$ band with the C-S stretching mode, with the 727 cm$^{-1}$ mode likely to be the out-of-plane methyl rock. However, a previous vibrational normal mode analysis [Byler and Gerasimowicz, J. Mol. Struct. 112 (1984) 207-219] showed strong coupling between the C-S stretch and CSH bending modes. They assign the 644 cm$^{-1}$ band to the latter, and attribute the C-S stretch instead to a feature at 688 cm$^{-1}$ that we find no clear evidence for in our spectrum. For normal CH$_{3}$SH, the CSH bend is very weak and lies between the strong C-S stretch and CH$_{3}$-rocking bands. A Gaussian quantum chemistry calculation of the vibrational frequencies and transition moments was carried out, and indeed there is a mode predicted to lie in between our two observed bands with almost vanishing intensity and a reduced mass and effective force constant corresponding closely to those calculated for the C-S stretch of normal CH$_{3}$SH. This apparent dramatic extinction of the normally very strong C-S stretching band is quite remarkable!
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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 | 0.001 |
| 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".