Probing the H–D isotopic exchange reaction in a liquid droplet via surface plasmon resonance

Abstract

The optical excitation of plasmonic oscillation at the metal–dielectric interface has widely been utilized for selective detection of molecules by tracking the change of the refractive index (RI) of the medium above the metal film. Here, we utilized the surface plasmon resonance (SPR) technique to explore the real-time kinetics of the H–D isotope exchange reaction between the hygroscopic D₂O droplet and atmospheric water (H₂O) vapour. These SPR experiments revealed new insights into the rate of exchange of D atoms (∼10¹⁷ atoms per s) and the time-scale for a single H–D exchange (∼few milliseconds) in a D₂O/H₂O medium under the experimental conditions of the present study. Unique SPR profiles were obtained for different mixtures of H₂O and D₂O, which were supported by respective RI measurements of the mixtures using a standard refractometer. The study also demonstrated the feasibility of SPR as a powerful method for real-time monitoring of temporal degradation of D₂O and detecting the impurity of water content in D₂O and vice versa.