Intertwined Electron and Proton Hopping: Synergistic experimental and theoretical approaches – IEPH

Pulse radiolysis
Density Functional Theory
Nuclear Electronic DFT

Expérimental study showing the ultrafast reduction of Ag+ in pulse radiolysis experiments.
Computational simulation of the reactivity of HEO+ in water.
First implementation of NEO-DFT in demon2k.

Exploring the reactivity of new species like I3-
terminating the implementation of auxiliary fittting technique for NEO-DFT

Unexpected Ultrafast Silver Ion Reduction: Dynamics Driven by the Solvent Structure. J. Phys. Chem. B. 2015, 119, 10096.

Electron and proton transfers (resp. ET and PT) are ubiquitous chemical reactions in the condensed phase. Both kinds of transfers are actually frequently interwoven in common chemical processes and are associated with a multitude of limiting physicochemical mechanisms. In addition owing to the small mass of both particles (especially electrons) quantum tunneling is an important feature of ET and PT that needs to be taken into account. The Marcus theory (MT) has inspired a variety of conceptual kinetics theories for interpreting pure PT, pure ET reactions or coupled proton coupled ET (PCET). However the physicochemical descriptions commonly in use cannot be seen as entirely satisfactory: unified frameworks for rationalizing all kinds of PET processes (pure ET, pure PT, stepwise EPT, PCET…) are still awaited. Going beyond the state-of-the-art is a challenging objective for computational or experimental approaches. Yet it is the principal objective of the IEPH project to lift the current methodological locks that have precluded a fine understanding of PET reactions in terms of elementary processes. Our approach will combine state-of-the-art computational and experimental tools in a synergistic manner.
We have recently developed in our Laboratory an experimental set-up based on the pulsed radiolysis for monitoring the scavenging of solvated electrons by small organic or inorganic molecules. Compared to other approaches our experimental set-up offers the unique opportunity i) to reach a very short time scales (< 100ps) and ii) to investigate ET, PT or PET between ground states. An ambitious experimental program will be unwounded during which we will investigate the rates of reaction between hydrogen atoms and organic/inorganic molecules: pure electron transfer, H-addition or H-abstraction reactions will be considered. In the reactions we will study, the PET is faster than the typical diffusion time so that the rates of the very PET processes are not known experimentally, hence the importance of our experimental set-up.
The experimental outputs of this experimental program will be interpreted through a set of innovative computational tools. The computational developments will combine two recent approaches: the 'Nuclear Electronic Orbital DFT' (NEO-DFT) and the 'constrained DFT'' (cDFT) methods. On one hand the NEO-DFT enables the protons and the electrons to be treated on equal footing, that is, at the quantum mechanical level. On the other hand cDFT is one of the very few quantum chemistry approaches enabling the definition of non-adiabatic states that resemble as much as possible to the phenomenological Marcus Theory states, and to evaluate quantities in direct connection to the experimental counterparts. These methods will be implemented in the Auxiliary DFT program deMon2k building on the valuable experience in DFT techniques (especially constrained and Auxiliary DFT) of the coordinator of the IEPH project. The newly implemented NEO-cDFT will be interfaced to Molecular Mechanics packages for hybrid QM/MM computations, thereby opening the door toward the modeling of ET, PT and PET with explicit inclusion of the system environment.
In summary, by providing us with an unprecedented combination of computational and experimental approaches, with no equivalent in Europe, the methodological developments of the IEPH project are expected to permit a breakthrough in the understanding of intertwined PET with high spatial and time resolutions.