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Caption : figure s1: raman spectra of solution a, solution b, solution c as well as their intermediary mixture and subsequent polyiodide spectrum. solution a, b and c were acquired with10 s exposure time over 9 s accumulations. the intermediary was acquired by accumulating 12 spectra in the intermediary phase. the end spectra were acquired by accumulating 161 spectra after the colour change had taken place. the elapsed spectra were acquired by accumulating 276 spectra after the spectra had reached a maximum. all spectra had their cosmic rays removed, were subsequently smoothed using savitzky–golay filtering, were baselined using asymmetric least squares, and were finally normalised and scaled.

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Caption : figure s2: a single briggs–rauscher cycle following the addition of solution c. (a) 16 evenly time spaced camera frames, with the boxed region indicating the pixel area used for hsv-luminosity analysis. (b) time-series in situ raman spectra showing the transition from solutions a + b through the addition of solution c to the subsequent rapid polyiodide formation. (c) in situ raman spectra (smoothed, baselined): left—overall polyiodide growth; right—autoscaled 400–1100 cm<sup>-1</sup> region highlighting the emergence of the 877 cm<sup>-1</sup> h<sub>2</sub>o<sub>2</sub> band, with the 802 and 980 cm<sup>-1</sup> modes remaining constant.

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Caption : figure s3: video screenshot of raman data alongside video footage of reaction. full video may be found in briggs_rauscher_run4_700c_0_5e_86p_1a_0i_baseline_l3.0_p5.0_animation_real_time_with_visual_side.mp4

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Caption : figure s4: ch<sub>2</sub>(cooh)<sub>2</sub> dependence on spectral contributions, (top) time-based dcls from addition of solution c, (bottom) corresponding fft of dcls.

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Caption : figure s5: kio<sub>3</sub> dependence on spectral contributions, (top) time-based dcls from addition of solution c, (bottom) corresponding fft of dcls.

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Caption : figure s6: time-matched in situ raman spectroscopic time-series br reaction at h<sub>2</sub>o<sub>2</sub> of 0.44 m.

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Caption : figure s7: h<sub>2</sub>o<sub>2</sub> dependence on spectral contributions, (top) time-based dcls from addition of solution c, (bottom) corresponding fft of dcls.

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Caption : figure s8: time-matched br reaction, (a) showing between final iodine spectral contribution and hsv value for the full br reaction in the absence of starch, (b) corresponding time-matched in situ raman spectroscopic time-series br reaction. time-matched in situ raman spectroscopic time-series br reaction. time-matched in situ raman spectroscopic time-series br reaction.