Real-Time Spectroscopic Insights into the Iodine Clock Reaction: Hidden Intermediates and Kinetic Delays

Tuesday, October 7, 2025

11:30 AM - 11:50 AM EDT

Location: Ballroom E

Presenting Author(s)

CG

CLARK GRAY

PhD Research Student
University of Liverpool
EDINBURGH, Scotland, United Kingdom

Non-Presenting Author(s)

NG

NIGEL GOTTS

University of Liverpool
LIVERPOOL, England, United Kingdom
CL

CASSIO LIMA, PhD

Research associate
University of Liverpool
LIVERPOOL, England, United Kingdom
KW

KENNETH WILLIAMS

Renishaw
Wotton-under-Edge, England, United Kingdom
SM

SEBASTIEN MAUSSANG

Renishaw
Champs-sur-Marne, Ile-de-France, France
RG

ROY GOODACRE, Prof

Professor
University of Liverpool
Liverpool, England, United Kingdom

In fifteen words or less, explain the significance of this contribution (Novel Aspect).: Real-time Raman spectroscopy reveals hidden intermediates and kinetics in the iodine clock and BR reaction.

Abstract Text: The iodine clock and Briggs–Rauscher (BR) reactions are iconic demonstrations of chemical kinetics and oscillations in chemistry education. Despite their widespread use, the real-time molecular dynamics underlying their colour changes remain poorly resolved. Here, we apply resonance Raman (RR) spectroscopy with 785 nm excitation to track the formation and interconversion of iodine species in both systems. In the iodine clock, we resolve the sequential appearance of iodide, iodine, and polyiodides (I₃⁻, I₅⁻), correlating spectral features with visible colour change and identifying a kinetic delay following sodium thiosulfate depletion. In the BR reaction, RR spectra reveal oscillatory behaviour through alternating intensities of triiodide (110 cm⁻¹) and pentaiodide (160 cm⁻¹), with Fourier analysis confirming periodic iodine speciation. We show that environmental variables—such as pH, temperature, and reagent concentration—govern the frequency and amplitude of both reactions, while starch modulates the dynamics by stabilising polyiodides. This study establishes RR spectroscopy as a precise, non-invasive tool for resolving the fast, coupled redox dynamics in visually striking kinetic systems, and could provide avenues for further chemical reactions and process monitoring.