Global Reaction Pathways in the Photodissociation of I₃⁻ Ions in Solution at 267 and 400 nm Studied by Picosecond X‐ray Liquidography

Abstract

The mechanism of a photochemical reaction involves the formation and dissociation of various short-lived species on ultrafast timescales and therefore its characterization requires detailed structural information on the transient species. By making use of a structurally sensitive X-ray probe, time-resolved X-ray liquidography (TRXL) can directly elucidate the structures of reacting molecules in the solution phase and thus determine the comprehensive reaction mechanism with high accuracy. In this work, by performing TRXL measurements at two different wavelengths (400 and 267 nm), the reaction mechanism of I3 (-) photolysis, which changes subtly depending on the excitation wavelength, is elucidated. Upon 400 nm photoexcitation, the I3 (-) ion dissociates into I2 (-) and I. By contrast, upon 267 nm photoexcitation, the I3 (-) ion undergoes both two-body dissociation (I2 (-) +I) and three-body dissociation (I(-) +2I) with 7:3 molar ratio. At both excitation wavelengths, all the transient species ultimately disappear in 80 ns by recombining to form the I3 (-) ion nongeminately. In addition to the reaction dynamics of solute species, the results reveal the transient structure of the solute/solvent cage and the changes in solvent density and temperature as a function of time.

Determining the charge distribution and the direction of bond cleavage with femtosecond anisotropic x-ray liquidography

“…1a ). Moreover, although it is known that I 2 − and I are formed by the excitation with 400 nm wavelength 31 , it is still elusive which specific bond dissociates among the two I–I bonds in I 3 − (Fig. 1b ).…”

Probing the molecular structure of aqueous triiodide via X-ray photoelectron spectroscopy and correlated electron phenomena

“…8,30,31,[50][51][52][53][54] The gas-phase anion is known to be a linear and centrosymmetric molecule. [32][33][34][35][36]55 However, upon dissolution in protic solvents, an asymmetry emerges in the terminal (t) to central (c) iodine atom bond lengths, 8,30,31,46,49,50,56 with this asymmetry increasing in going from an ethanol to a methanol and then an aqueous solvent. 31,50 This asymmetry increase has been correlated with the increasing hydrogen-bond-donor capabilities of the respective solvents.…”

Tracking reaction dynamics in solution by pump–probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering)

“…105,106,110,137 3.2 Application of TRXL TRXL has been used to capture the molecular structures of transient intermediates and their spatiotemporal kinetics for various photochemical processes. The molecular systems studied by TRXL spans from small molecules [79][80][81][82]84,85,[87][88][89]92,93,98,99,[105][106][107][110][111][112]114,115,128,[130][131][132][133]136,140 to organometallic complexes, 97,103,104,109,113,116,119,124,141 nanoparticles, 83,86,90,91,94,95,100,120,…”