Inelastic electron tunnelling in saturated molecules with different functional groups: correlations and symmetry...

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• Inelastic Electron Tunnelling (IET) spectroscopy is a sensitive surface science technique.
• Identifying functional groups within molecules is crucial for understanding molecular interactions and electronic properties.
• Previous studies have explored the potential of IET for molecular identification, but comprehensive computational validation is needed.

Purpose of the Study:

• To computationally evaluate the Inelastic Electron Tunnelling (IET) spectra of molecules containing common functional groups.
• To determine which functional groups provide characteristic signatures in IET spectra for use as electronic tracers.
• To validate existing propensity rules for IET spectroscopy using saturated molecules.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to simulate IET spectra.
• A series of molecules with varying functional groups (ether, amine, thioether, carbonyl, ester) were computationally analyzed.
• The simulated IET spectra were compared to identify characteristic spectral modifications.

Main Results:

• Ether, secondary amine, and thioether groups showed no distinct spectral signatures compared to alkanes, limiting their use as IET tracers.
• Carbonyl and ester groups significantly modified the IET spectra, indicating their potential for spectral identification.
• Computational results validated propensity rules, showing that totally symmetric vibrations yield the largest spectral contributions.
• No correlation was found between IET spectral intensities and infrared or Raman absorption intensities.

Conclusions:

• Carbonyl and ester groups are suitable tracers for electron tunnelling paths in IET spectroscopy due to their distinct spectral modifications.
• Ether, amine, and thioether groups are not effective tracers in IET spectroscopy.
• Totally symmetric vibrations are the primary contributors to IET spectra, and IET intensity does not correlate with IR or Raman intensities.