The Structural Characterization Of Solvated Electron And Its Associated Properties Revealed By Theoretical Studies

The solvated electron,which usually distributes at a place relatively far away from the molecular framework,has attracted intense interest in the past few decades due to its important role in many physical,chemical and biological processes.This weakly-bound excess electron has been extensively investigated by various methods,and many important applications to charge transfer,radical reactions,and polarons follow from their special physical characterization and reactivity.Although significant efforts have been made to understand the convoluted solvent effects and the nature of the solvated electrons,many debates still remain,and interest in the fundamental processes involved in the reactivity of trapped electrons continues.Accordingly,in this work,the systematic investigations of the special electronic and structural properties of the solvated electrons are performed by means of quantum mechanical calculations,the time-dependent wave-packet study and the ab initio molecular dynamics simulations.In addition,the mechanism of the dissociative electron attachment of the selected tumor-specific sensitizer,5-BrPy,is also discussed in detail.The primary innovations are related as follows.(1)The solvated electron usually bound weakly in intermolecular zones far away from the nuclei,and thus the diffuse function requirement may turn out to be more urgent or important for the solvated electrons due to their extremely diffuse characters.To examine the effects of diffuse functions on the nature of the cavity-shaped solvated electrons in water cluster surroundings,both the HOMO and LUMO distributions,vertical detachment energies(VDEs)and visible absorption spectra of two selected(H2O)24-isomers are investigated.The present work reveals that:(a)augmentation of atom centered diffuse functions is favorable to the VDE convergence,but also leads to an unreasonable description of the LUMO,and thus causes a significant red shift in the vis spectrum;(b)extra floating diffuse functions are necessary not only for reducing the computational cost but also for providing a practical way to avoid excessive augmentation of the atom-centered diffuse functions and give correct LUMO distributions as well as the corresponding UV-vis spectroscopic absorption.This work presents an efficient way for characterizing the electronic properties of weakly bound electrons accurately by balancing the addition of atom-centered diffuse functions and floating diffuse functions,and thus is very useful in the relevant calculations of various solvated electron systems and weakly bound anionic systems.(2)The water cluster anions with surface-bound solvated electrons,which present more diffuse characteristics than interior-bound species,have been proved to be preferential for small(H2O)-n,and also responsible for clusters as large as n = 24.Such a character of the weakly bound systems requires more diffuse functions in relevant calculations.In this work,the effect of diffuse function types(atom-centered diffuse functions versus floating functions and s-type versus p-type diffuse functions)on the structures and properties of three representative water cluster anions featuring a surface-bound solvated electron is studied and we find that an effective combination of such two kinds of diffuse functions can not only reduce the computational cost but also,most importantly,considerably improve the accuracy of results and even avoid incorrect predictions of spectra and the electronic distribution.This work provides general recommendations for the basis set choices appropriate for the calculations of various water cluster anions featuring the surface-bound solvated electron,(H2O)-n,or other solvent cluster anions and the solvated electrons in condensed media in both energetics and spectra.(3)While the optics and conductance behavior induced by the solvated electron in corresponding compounds have been investigated successfully,insight into the magnetic properties(especially the nuclear spin-spin couplings)of such solvated electron coupled anionic systems is still scarce.The present wok reports the theoretical prediction of the influence caused by the solvated electron on the spin-spin coupling constants in fluoro-cluster anions.DFT calculations reveal that the solvated electron in clusters possesses exceptionable large JFF-couplings than those of its corresponding neutral backbone.Obviously,the solvated electron is the key factor in bringing to the corresponding cluster anions significantly large JFF couplings.The magnitudes of variation are closely related to the solvated electron binding states,i.e.,the JFF-couplings are in direct proportion to the covalent characters along the coupling pathway(e-bond),and also dependent strongly on the charge exchange between the solvated electron and HF subunits.This work provides comprehensive understanding of the solvated electron-induced systematic trends of J-couplings and may also contribute to a probe of the solvated electrons in future studies.(4)Radiation-generated secondary electrons can induce resonance processes in a target molecule and fragment it via different pathways.Although the associating electronic resonant states at equilibrium geometry have been well studied for many target molecules,the dynamic details and the solvent effect are still poorly understood.Taking a radiosensitive drug,5-bromopyrimidine(5-BrPy),as an example,we here present a combined ab initio molecular dynamics simulation and time-dependent wave packet study with an emphasis on vibrational resonance and solvation effects on excess electron interaction with 5-BrPy.The gaseous results reveal two primary channels for the electron induced C-Br bond cleavage:the highest vibrational resonance on vertical potential energy curve via a tunneling mechanism,and auto-dissociation along repulsive relaxed potential energy curve,which account for the two peaks at 0.2 and 0 eV observed in Modelli’s experiment.However,a strong solvation effect modifies the mechanism and dynamics of the dissociation of the electron 5-BrPy system.On one hand,the spontaneous dissociation becomes unfavorable due to a barrier on the relaxed free energy surface created by the coupling between the π*and a*states.On the other hand,protonation is also observed at the N sites of the hydrated 5-BrPy anion,and this inhibits the dissociation along the C-Br bond,suggesting a competing pathway against C-Br bond cleavage.This work provides a deep understanding of the radio-sensitivity of the 5-BrPy drug in solution and reveals the important impact of the low energy electron triggered vibrational excitations and also the importance of the solvent effect.