# Submolecular‐Resolution Probing of Vibrational Anharmonicity Using Tip‐Enhanced Raman Spectroscopy

## TL;DR

Scientists used a specialized Raman technique to detect vibrational energy at submolecular resolution, revealing new insights into molecular energy transfer.

## Contribution

The study introduces submolecular-resolution detection of vibrational anharmonicity using tip-enhanced Raman spectroscopy.

## Key findings

- Tip-apex contact enhances Raman peaks by ∼10 times, enabling detection of overtones and combination bands.
- Two types of anharmonicity are resolved: mechanical and electrical, with submolecular contrast.
- Spatial variation of mechanical anharmonicity reveals vibrational energy exchange at the submolecular scale.

## Abstract

Vibrational spectroscopy can reach atomic spatial resolution via highly confined optical probes, offering local chemical insight. Yet, overtones and combination bands have not fully benefited due to weak transition moments. Here, we show submolecular‐resolution detection of intense overtones and combination bands using tip‐enhanced Raman spectroscopy (TERS) for an asymmetric perylene derivative on silicon. The Raman peaks, barely visible in tunneling regime, are ∼10 times enhanced when the tip‐apex contacts the molecule. This point‐contact‐mode TERS enables analysis of two anharmonicities with submolecular contrast: one arising from deviations of potential energy surfaces from harmonic shape (mechanical anharmonicity), the other from high‐order polarizability derivatives (electrical anharmonicity). Spatial variation of mechanical anharmonicity reveals a vibrational energy exchange channel at the submolecular scale, highlighting potential to map energy transfer in real space.

This work explores how tip‐enhanced Raman spectroscopy achieves submolecular resolution in detecting vibrational overtones and combination bands. This breakthrough reveals site‐specific anharmonicities and energy transfer pathways within single molecules, advancing chemical analysis with unprecedented spatial and spectral detail.