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Tracking structural solvent reorganization and recombination dynamics following e - photoabstraction from aqueous I - with femtosecond x-ray spectroscopy and scattering.
- Source :
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The Journal of chemical physics [J Chem Phys] 2022 Dec 14; Vol. 157 (22), pp. 224201. - Publication Year :
- 2022
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Abstract
- We present a sub-picosecond resolved investigation of the structural solvent reorganization and geminate recombination dynamics following 400 nm two-photon excitation and photodetachment of a valence p electron from the aqueous atomic solute, I <superscript>-</superscript> (aq). The measurements utilized time-resolved X-ray Absorption Near Edge Structure (TR-XANES) spectroscopy and X-ray Solution Scattering (TR-XSS) at the Linac Coherent Light Source x-ray free electron laser in a laser pump/x-ray probe experiment. The XANES measurements around the L <subscript>1</subscript> -edge of the generated nascent iodine atoms (I <superscript>0</superscript> ) yield an average electron ejection distance from the iodine parent of 7.4 ± 1.5 Å with an excitation yield of about 1/3 of the 0.1M NaI aqueous solution. The kinetic traces of the XANES measurement are in agreement with a purely diffusion-driven geminate iodine-electron recombination model without the need for a long-lived (I <superscript>0</superscript> :e <superscript>-</superscript> ) contact pair. Nonequilibrium classical molecular dynamics simulations indicate a delayed response of the caging H <subscript>2</subscript> O solvent shell and this is supported by the structural analysis of the XSS data: We identify a two-step process exhibiting a 0.1 ps delayed solvent shell reorganization time within the tight H-bond network and a 0.3 ps time constant for the mean iodine-oxygen distance changes. The results indicate that most of the reorganization can be explained classically by a transition from a hydrophilic cavity with a well-ordered first solvation shell (hydrogens pointing toward I <superscript>-</superscript> ) to an expanded cavity around I <superscript>0</superscript> with a more random orientation of the H <subscript>2</subscript> O molecules in a broadened first solvation shell.
Details
- Language :
- English
- ISSN :
- 1089-7690
- Volume :
- 157
- Issue :
- 22
- Database :
- MEDLINE
- Journal :
- The Journal of chemical physics
- Publication Type :
- Academic Journal
- Accession number :
- 36546808
- Full Text :
- https://doi.org/10.1063/5.0107224