Stepwise Hydration of Protonated Carbonic Acid: A Theoretical Study (original) (raw)
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Journal of The American Society for Mass Spectrometry
Protonation, hydration, and cluster formation of ammonia, formaldehyde, formic acid, acetone, butanone, 2-ocatanone, 2-nonanone, acetophenone, ethanol, pyridine, and its derivatives were studied by IMS-TOFMS technique equipped with a corona discharge ion source. It was found that tendency of the protonated molecules, MH + , to participate in hydration or cluster formation depends on the basicity of M. The molecules with higher basicity were hydrated less than those with lower basicity. The mass spectra of the low basic molecules such as formaldehyde exhibited larger clusters of M n H + (H 2 O) n , while for compounds with high basicity such as pyridine, only MH + and MH + M peaks were observed. The results of DFT calculations show that enthalpies of hydrations and cluster formation decrease as basicities of the molecules increases. Using comparison of mass spectra of formic acid, formaldehyde, and ethanol, effect of structure on the cluster formation was also investigated. Formation of symmetric (MH + M) and asymmetric proton-bound dimers (MH + N) was studied by ion mobility and mass spectrometry techniques. Both theoretical and experimental results show that asymmetric dimers are formed more easily between molecules (M and N) with comparable basicity. As the basicity difference between M and N increases, the enthalpy of MH + N formation decreases.
Chemical Physics, 2011
We present a theoretical study of the structure and dynamics of protonated water clusters by means of quantum chemical calculations and ab initio molecular dynamics simulations. We have considered the clusters H + (H 2 O) n for four different sizes corresponding to n = 5, 9, 17 and 21. We have first looked at the solvation states of the excess proton in several lower energy structures of these clusters with a special interest in finding its surface versus interior states and its hydrogen bonding environment. Subsequently, we have investigated the finite temperature behavior of these clusters through ab initio simulations. We have looked at vibrational spectral features with special emphasis given to the spectral features of free OH (deuterated) modes and their dependence on donor-acceptor hydrogen bonding states of the water molecules. We have also investigated the mechanism and kinetics of proton transfer events in these clusters by using a population correlation function approach.
Chemical Physics, 2012
We present a theoretical study of the structure and dynamics of protonated water clusters by means of quantum chemical calculations and ab initio molecular dynamics simulations. We have considered the clusters H + (H 2 O) n for four different sizes corresponding to n = 5, 9, 17 and 21. We have first looked at the solvation states of the excess proton in several lower energy structures of these clusters with a special interest in finding its surface versus interior states and its hydrogen bonding environment. Subsequently, we have investigated the finite temperature behavior of these clusters through ab initio simulations. We have looked at vibrational spectral features with special emphasis given to the spectral features of free OH (deuterated) modes and their dependence on donor-acceptor hydrogen bonding states of the water molecules. We have also investigated the mechanism and kinetics of proton transfer events in these clusters by using a population correlation function approach.
A bond-order analysis of the mechanism for hydrated proton mobility in liquid water
Chemical Physics, 2005
Bond-order analysis is introduced to facilitate the study of cooperative many-molecule effects on proton mobility in liquid water, as simulated using the multistate empirical valence-bond methodology. We calculate the temperature dependence for proton mobility and the total effective bond orders in the first two solvation shells surrounding the H5O2+ proton-transferring complex. We find that proton-hopping between adjacent water molecules proceeds via this intermediate, but couples to hydrogen-bond dynamics in larger water clusters than previously anticipated. A two-color classification of these hydrogen bonds leads to an extended mechanism for proton mobility.
Pramana, 2005
The hydration structure and translocation of an excess proton in hydrogen bonded water clusters of two different sizes are investigated by means of finite temperature quantum simulations. The simulations are performed by employing the method of Car-Parrinello molecular dynamics where the forces on the nuclei are obtained directly from 'on the fly' quantum electronic structure calculations. Since no predefined interaction potentials are used in this scheme, it is ideally suited to study proton translocation processes which proceed through breaking and formation of chemical bonds. The coordination number of the hydrated proton and the index of oxygen to which the excess proton is attached are calculated along the simulation trajectories for both the clusters.
A Density Functional Theory for Studying Ionization Processes in Water Clusters
The Journal of Physical Chemistry A, 2011
A generalized Kohn-Sham (GKS) approach to density functional theory (DFT), based on the Baer-Neuhauser-Livshits range-separated hybrid, combined with ab initio motivated range-parameter tuning is used to study properties of water dimer and pentamer cations. The water dimer is first used as a benchmark system to check the approach. The present brand of DFT localizes the positive charge (hole), stabilizing the proton transferred geometry in agreement with recent coupled-cluster calculations. Relative energies of various conformers of the water dimer cation compare well with previously published coupled cluster results. The GKS orbital energies are good approximations to the experimental ionization potentials of the system. Low-lying excitation energies calculated from time-dependent DFT based on the present method compare well with recently published high-level "equation of motion-coupled-cluster" calculations. The harmonic frequencies of the water dimer cation are in good agreement with experimental and wave function calculations where available. The method is applied to study the water pentamer cation. Three conformers are identified: two are Eigen type and one is a Zundel type. The structure and harmonic vibrational structure are analyzed. The ionization dynamics of a pentamer water cluster at 0 K shows a fast <50 fs transient for transferring a proton from one of the water molecules, releasing a hydroxyl radical and creating a protonated tetramer carrying the excess hole.