Polarizability-Induced Vibrational Shifts for Infrared Spectroscopy of Molecular Surfaces: Xe as a Surface Probe of Hexadecanethiol Self-Assembled Monolayers and Hexane Films on Au(111)
Bibliographic record
Abstract
Adsorption of atomic and molecular species on several model film surfaces is shown to lead to systematic and reproducible spectral shifts for infrared absorption peaks associated with vibrations at the film/adsorbate interface. These shifts to lower frequencies are demonstrated to be versatile spectral signatures of this exposed interface. While this is found to occur for a wide variety of adsorbates, this work focuses on the adsorption of Xe onto molecular surfaces. By using the pre-Xe film reflectivity as a reference in calculating the spectra, the changes induced by Xe adsorption due to van der Waals forces are isolated from the conventional film spectrum which contains both surface and subsurface spectral contributions. A model-free algorithm containing two user-defined fitting parameters is described to reconstruct the spectrum of the surface from which these shifted features originate. The high surface sensitivity of the technique is exhibited for the case of a hexadecanethiol self-assembled monolayer (SAM), where the reconstruction algorithm successfully reproduces all peaks attributed to the methyl tail groups with minimal spectral contributions from the methylene groups composing the subsurface chain backbone; such methylene spectral features dominate the conventional surface infrared spectra. The algorithm is applied to films of hexane to demonstrate its application to disordered multilayer films as well. The technique and reconstruction algorithm are shown to extract spectroscopic information from the uppermost ∼0.3 nm of the film, representing the fundamental limit of vibrational surface sensitivity. Rudimentary modeling of a CO-Xe 3 system using Morse/Lennard-Jones interactions demonstrates the expected distance dependence of the van der Waals interaction which gives rise to the observed vibrational spectral shifts.
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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) | 0.001 | 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".