Visualization of hydrogen isotope exchange in single molecule by tip-enhanced Raman images

Abstract

Intramolecular hydrogen isotope exchange (HIE) plays a pivotal role in regulating molecular photoelectric properties, reaction pathways, and kinetic control. However, due to intrinsic limitations of conventional techniques, direct real-space observation of the atom-by-atom HIE process at the single-molecule level remains challenging, as does the difficulty of accurately counting and locating intramolecular isotope-substituted atoms. Herein, taking the experimentally accessible coronene as a model system, we theoretically demonstrate the capability of tip-enhanced Raman scattering (TERS), modulated by vibrational interference between atomic motions in a given normal mode, to distinguish and identify various hydrogen-to-deuterium isotope substitution configurations. By overlaying mode-specific TERS images at characteristic vibrational frequencies, our approach allows precise determination of the number, spatial positions, and isotopic categories (deuterium/tritium) of exchanged atoms in an individual molecule. These findings establish TERS imaging as a powerful technique to directly visualize intramolecular isotopic transformations, providing new insights into quantum vibrational dynamics and interference-mediated reaction pathways at the nanoscale.