Atomically-Resolved Structural Changes During Triiodide Anion Photodissociation

XIAN, R.; HAYES, S. A.; CORTHEY, G.; MORRISON, CAROLE A.; ROGERS, DAVID M.; MARX, A.; PROKHORENKO, VALENTYN I.; MILLER, R. J. D.

Banff

Congreso; 5th Banff Meeting on Structural Dynamics; 2017

Understanding physical and chemical processes from the ground up requires a structure-sensitive probe fast enough to resolve atomic displacements.1 Femtosecond electron diffraction has emerged as a key technique in this perspective. It has recently become possible to reconstruct atomically-resolved dynamics of a solid-state phase transition from time-resolved diffraction data.2 Pushing the frontier further into studying chemical processes requires tackling issues such as limited reversibility3 and low signal count. As a test example, we investigated the photodissociation and recombination of the triiodide ion (I3−) in single-crystal tetra-n-butylammonium triiodide and, in this poster, we will discuss a joint investigation of this reaction using broadband transient absorption spectroscopy and femtosecond electron diffraction.Previous studies of the triiodide photochemistry in the gas phase and in solution used flowing samples to bypass the inherent irreversibility of the reaction. Extension of the study to the solid state has been hampered by the slow and incomplete regeneration of reactants and the difficulty of preparing thin samples. Therefore, only a single-shot spectroscopy experiment has been performed using single-color pump and tunable probe pulses.4 Moreover, the spectral overlaps of I3− and the transient intermediates, such as the photofragments I2−?, I?, I−, etc., also call for an independent investigation other than transient absorption (TA) experiments. To minimize the sample limitations, we used microtomed thin samples and stabilized the sample temperature. These improvements on the measurement conditions allowed us to record time-resolved dynamics in a stroboscopic manner. The results provide evidence of the atomic origins of the coherent modes driven by the reaction.5(1) R. J. D. Miller et al. Acta Cryst. A 66, 137-156 (2010).(2) T. Ishikawa, S. A. Hayes, et al. Science 350, 1501-1505 (2015).(3) H. Jean-Ruel et al. J. Phys. Chem. B 117, 15894-15902 (2013).(4) P. Poulin and K. Nelson, Science 313, 1756-1760 (2006).(5) Xian, R. et al. Nat. Chem. In press.