T-jump spectroscopy was carried out at the Rutherford-Appleton Laboratory Ultra facility using a variation on the TRMPS technique. The experiment is shown in Figure . To adequately cover the ν(CH) and ν(OD) modes of the vibrational spectrum, probe pulses centred at ca. 2700 cm -1 with a useable bandwidth > 500 cm -1 and an energy of 1-2 J / pulse were generated at 10 kHz by difference frequency mixing the output of an Optical Parametric Amplifier (OPA, Light Conversion TOPAS) pumped by 5 W of 800 nm light sourced from a 20 W, 50 fs Ti:Sapphire amplifier system (Coherent Legend Elite Duo). Pump pulses of ~ 110 μJ energy and < 1.5 ns duration centred at 3600 cm -1 were generated using 2 mJ of light from a Nd:YAG (BrightSolutions Wedge, 1 kHz, 4 mJ) pumping a home-built OPO based on periodically poled lithium niobate (PPLN, Covesion) heated to 75 °C to give an OPO output of 3600 cm -1 with a pulse duration < 1.5 ns. In Figure , the pump laser is synchronised to the probe laser and operated at repetition rates from 2 Hz to 1 kHz. High-voltage Q-switch noise from the pump laser coupling into the IR detection system is subtracted using a chopper operating at half the pump repetition rate, giving a 'pump-off' dataset for each entire TRMPS probe sequence. The longest TRMPS time delay measurable is then half the pump pulse period. The 10 kHz probing gives multiple probe pulses spaced by 100 s. To achieve sub-100 μs time resolution on the first probe pulse of the sequence, the pump-probe pulse timing | 3 is controlled by triggering the Nd:YAG Q-switch at a fixed delay set by a computer controlled electronic pulse delay generator (Stanford DG465). This pulse generator could also trigger the Nd:YAG laser to make bursts of pulses, each burst treated like a single pump event. For the data in this paper, TRMPS spectra for a given electronic delay were averaged for 30 -60 seconds. Further details regarding the triggering of the chopper, sample stage movement and pump bursts are described in ESI Section 2.