Revealing Intramolecular Isotope Effects with Chemical-Bond Precision

Isotope substitution of a molecule not only changes itsvibrationalfrequencies but also changes its vibrational distributions in real-space.Quantitatively measuring the isotope effects inside a polyatomic moleculerequires both energy and spatial resolutions at the single-bond level,which has been a long-lasting challenge in macroscopic techniques.By achieving a ngstro''m resolution in tip-enhanced Ramanspectroscopy (TERS), we record the corresponding local vibrationalmodes of pentacene and its fully deuterated form, enabling us to identifyand measure the isotope effect of each vibrational mode. The measuredfrequency ratio & nu;(H)/& nu;(D) varies from1.02 to 1.33 in different vibrational modes, indicating differentisotopic contributions of H/D atoms, which can be distinguished fromTERS maps in real-space and well described by the potential energydistribution simulations. Our study demonstrates that TERS can serveas a non-destructive and highly sensitive methodology for isotopedetection and recognition with chemical-bond precision.

Automated summary

Isotope substitution not only changes the vibrational frequencies but also the vibrational distributions in real-space of a molecule. Measuring isotope effects in a polyatomic molecule at the single-bond level with energy and spatial resolutions has been challenging. By achieving angstrom resolution in tip-enhanced Raman spectroscopy (TERS), the isotope effect of each vibrational mode in pentacene and its fully deuterated form is identified and measured. The frequency ratio ν(H)/ν(D) varies from 1.02 to 1.33, indicating different isotopic contributions of H/D atoms, which can be distinguished and described by TERS maps and potential energy distribution simulations. This study demonstrates that TERS can be a non-destructive and highly sensitive method for isotope detection and recognition with chemical-bond precision.