A theoretical approach exploiting molecular dynamics simulations to treat adiabatic proton transfer between an acid AH and a base B in a polar, aprotic solvent is presented. The dynamics of the proton transfer, which occurs on the electronic ground state surface of the reactive hydrogen-bonded complex AH...B, is strongly influenced by interaction of the reaction system with the solvent and by the AB stretch vibration. The approach fully incorporates the quantum character of the proton motion as well as that of the AB stretch vibration and yields a mechanistic picture for a thermally activated proton transfer reaction in a polar solvent. Rate constants are computed and solvent frictional effects are analyzed in application of the theory to a model of the system phenol-trimethylamine in methyl chloride solvent. In addition, it is shown how the excitation of the hydrogen bond symmetric stretch mode decelerates the reaction. The simulation results are also compared to a curve-crossing model. The impact of the solvent electronic polarization on the results is discussed.
For mixed quantum-classical molecular dynamics simulations of solvated excess charges a novel and efficient method to expand the solute electronic wave function in a distributed Gaussian basis with a shell structure is presented. The aggregate of Gaussian orbitals is capable of mimicking the shape fluctuation of the excess charge distribution and its diffusion through the solvent. This approach also offers an easy pathway to treat the solvent electronic polarization in an explicit and self-consistent fashion. As applications, the results of adiabatic molecular dynamics simulations for the hydrated electron and the aqueous chloride are reported. For e−/H2O the computed ground state absorption spectrum is discussed. Adiabatic relaxation as well as nonadiabatic transition rates are evaluated—the latter by means of an original Golden Rule formula—and compared to experimental results. In the case of Cl−/H2O the charge transfer to solvent spectra are analyzed. The ability of the mobile basis set method to describe the photodetachment dynamics of an electron from aqueous chloride is also demonstrated.
Reaction and relaxation processes induced by photoexcitation of an aqueous chloride ion are studied with quantum molecular dynamics simulations. A predominant channel leading to a metastable hydrated electron-chlorine pair is found. By means of theoretical transient and stationary absorption spectra, the solvent reorganization involved in the charge repartitioning is discussed. The dissipation of excess electron kinetic energy by surrounding water molecules plays an essential role in the equilibration of an electron-atom pair. For this intermediate species, two competing reaction pathways are identified. One is the barrier-impeded dissociation yielding a hydrated electron. Shape and height of the free energy barrier determined by quantum umbrella sampling point to a diffusion controlled electron photodetachment. The other channel is the geminate recombination via a nonadiabatic transition for which a self-consistent and fully dynamical treatment of the solvent electronic polarization is found to be important. From the rate constants computed for the individual channels, a kinetic model is derived to explain time-dependent spectral signatures and electron escape yields recently observed in photodetachment experiments on aqueous halides.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.