Molecular dynamic simulation of the structure of water in the vicinity of a solvated ion

Rao, M. Nageswara; Berne, B. J.

doi:10.1021/j150611a010

Cited by 67 publications

(22 citation statements)

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“…Both HPMS studies l3 -15 and a recent kinetic fragmentation study of ammonia cluster ions by Castleman and coworkers 34 indicate that differences up to 10% are possible. However, as will be seen below, the unimolecular dissociation rate is the most important factor in the cluster-ion photodissociation, and variations in V 25 have virtually no effect on k25 (E). The variation of the frequency prefactor A has little effect on either the average energy or dissociation rate.…”

Section: L=6a-3mentioning

confidence: 92%

Gas-phase methanol solvation of Cs+ : Vibrational spectroscopy and Monte Carlo simulation

Draves

Luthey‐Schulten

Liu

et al. 1990

The Journal of Chemical Physics

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The solvation of the cesium ion by methanol has been investigated by gas-phase vibrational spectroscopy and Monte Carlo simulations of small ion clusters: Cs( CH 3 OH): , N = 4-25. The solvated ions, generated by thermionic emission and a molecular-beam source, have considerable amounts of internal energy. After excessive energy is dissipated by evaporation, quasistable cluster ions are mass-selected for vibrational predissociation spectroscopy using a line-tunable cw-C0 2 laser. Analysis of the vibrational spectra indicates that the first solvation shell about the cesium ion consists often methanol molecules. Larger Cs(CH 3 OH): (N) 18) appear to have small clusters of methanol bound to the surface of a solvated ion. Monte Carlo simulations using pairwise interaction potentials at 200, 250, and 300 K have been performed on Cs(CH 3 0H):, N = 6-16 and 25. The results from the simulations are consistent with the observed solvent shell size and suggest a significant role for hydrogen bonding in the larger solvated ions (N;;.lO). Once the first solvation shell is filled, the size of the solvent shell appears to be independent of the number of additional solvent molecules. Gas-phase solvated ions appear to be extremely useful models for dilute electrolyte solutions.

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Section: L=6a-3mentioning

confidence: 92%

Gas-phase methanol solvation of Cs+ : Vibrational spectroscopy and Monte Carlo simulation

Draves

Luthey‐Schulten

Liu

et al. 1990

The Journal of Chemical Physics

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“…39 For the solutes involved in charge-transfer reactions that undergo a change in oxidation state, the addition or removal of electrons can make the effective change in size even larger. 40 Thus, the most realistic case to consider is that of a solute that undergoes a simultaneous change in both size and charge; modeling only the change in charge or size misses a great deal of the essential physics. In our previous paper, we explored the equilibrium solvent dynamics for coupled size-and-charge changes and found that the nature of the solvent response depends on both the magnitude and the sign of the size and charge changes involved.…”

Section: Breakdown Of Linear Response For Nonpolar Solvationmentioning

confidence: 99%

Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

2000

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The fact that the motion of solvent molecules defines the reaction coordinate for electron-transfer and other chemical reactions has generated great interest in solvation dynamics, the study of how the solvent responds to changes in a solute's electronic state. In the limit of linear response (LR), when the perturbation caused by the solute is "small", the relaxation of the excited solute's energy gap should behave identically to the relaxation dynamics of the unperturbed solute following a natural fluctuation of the gap away from equilibrium. Despite the fact that the addition of a fundamental unit of charge to a small solute results in a solvation energy that is tens or hundreds of kT, computer simulations of solvation dynamics have found, with only a few exceptions, that LR is obeyed for changes in solute charge. Essentially none of this work, however, accounts for the fact that the solutes in real chemical reactions undergo changes in size and shape as well as in charge distribution. In this paper, we compare the results of molecular simulations of polar and nonpolar solvation dynamics for a simple Lennard-Jones solute in a flexible-water solution to explore the validity of LR. We find that, when short-range forces are involved, LR breaks down dramatically: both the inertial and diffusive components of the relaxation differ from those predicted by LR. For increases in solute size, expansion of the solute drives the first-shell solvent molecules into the second shell. The resulting nonequilibrium relaxation takes advantage of translation-rotation coupling that does not occur at equilibrium, resulting in faster solvation than that predicted by LR. Decreases in solute size, on the other hand, result in inward translational motions of solvent molecules that affect the solute's energy gap by destabilizing the energy of the (unoccupied) ground state. The inward motions involved in the nonequilibrium relaxation are not present at equilibrium because the destabilization of the ground state is much larger than kT. Because the energetically most important solvent molecules, those closest to the solute, are just as likely to be moving away from the solute as toward it at the time of excitation, solvation for decreases in size is much slower than predicted by LR. In the most realistic cases, when both the size and the charge of the solute change, the solvent translational motions resulting from the size change and those resulting from electrostriction, the net ion-dipole attraction between the charged solute and the polar solvent, combine in an additive fashion. When the solute both gains a charge and expands, the translational motions resulting from electrostriction nearly cancel those from the outward solute expansion so that rotational motions dominate the solvent response; the small net expansion that remains results in only a minor breakdown of LR. The additional inward solvent translations beyond those required by electrostriction, which are necessary when the solute becomes charged and its size decreases, on the ...

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“…Theoretical treatments that go beyond continuum theory in fact predict multiexponential C(t) functions and relaxation components that are considerably longer than vl [65,88]. Apparently, these theoretical effects, which seem to parallel experiment, should be attributed to molecular motion of the solvent shells near the solute, but clearly more theoretical work involving continuum and noncontinuum models is necessary in this area.…”

Section: Transient Solvationmentioning

confidence: 98%

“…This is a critical time-scale, however, for friction on reactions in solution because the actual barrier crossing process occurs on the femtosecond time-scale. Furthermore, molecular simulations suggest that the femtosecond dynamics of C(t) are complicated and not characterizable by back extrapolating the long time-scale behavior of C(t) to earlier time [88]. Fortunately, experiments are in progress in our laboratory and elsewhere on transient solvation on the femtosecond time-scale, and results should be forthcoming in the near future.…”

Section: Transient Solvationmentioning

confidence: 99%

Ultrafast Measurements on Excited State Isomerization

Barbara

Walker

1988

Reviews of Chemical Intermediates

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The investigation of ultrafast isomerizations has been primarily limited to reactions in electronically excited molecules, because these are the easiest to study by ultrafast spectroscopy. Three reaction types have been popular, namely: (i) cis/trans isomerization and related large amplitude reactions in nonpolar environments, (ii) intramolecular electron transfer, and (iii) intramolecular proton transfer. The solute (reactant)/solvent interactions that are most relevant for these reactions differ. Specifically, short range repulsive interactions are most important for nonpolar cis/tran8 isomerization, polar interactions are most important for intramolecular electron transfer, and hydrogen bonding is the most important interaction for the intramolecular proton transfer. Theoretical work on these reaction types has gone beyond tst to schemes that allow for dynamic solute/solvent interactions and other more subtle effects. Experimental work has emphasized, where possible, an evaluation of the new theoretical frameworks for these three reaction types.The present report will review in Sections III-V our work on ultrafast cis/tran8 isomerizations, intramolecular electron transfer, and the related process the transient solvation of polar molecules in polar solvents. Research from our laboratory on excited state intramolecular proton transfer has been reviewed elsewhere [1]. Some of the elementary theoretical notions that are relevant to ultrafast isomerization are reviewed briefly in Section II. Throughout this paper an attempt will be made to highlight the state of knowledge in this rapidly developing field, which has had contributions from many researchers. Excellent reviews and well referenced articles that emphasize different aspects of ultrafast isomerizations can be found in the literature [2][3][4]. Much of the research we describe in this paper has been made possible by recent advances in the technology of ultrafast spectroscopy, particularly in the area of subpicosecond spectroscopy. However, technical details on the experimental apparatuses are beyond the scope of the present review and can be found elsewhere [5][6][7][8]. II. BEYOND TRANSITION STATE THEORY.According to the canonical tst the rate constant of a chemical reaction can be represented by the well-known relationship [9],where kB is Boltzmann's constant. A key assumption of the derivation of Eq. (1) is that if a reacting system is in the configuration of the transition state it will be converted to product with unit probability. Equation(1) can be inaccurate for solution phase reactions where dynamic solvent effects are non-negligible [10][11][12][13][14][15][16][17][18][19][20][21][22]. In simple terms, collisions between the solvent and reactant can induce recrossings of the barrier at the transition state. This will reduce the reaction rate. For such a case the true reaction rate constant k is related to k TM by Eq. (2) where ~ corrects the tst rate constant for non-tst effects such as solvent-induced barrier recrossings and other effects.Histori...

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Molecular dynamic simulation of the structure of water in the vicinity of a solvated ion

Cited by 67 publications

References 1 publication

Gas-phase methanol solvation of Cs+ : Vibrational spectroscopy and Monte Carlo simulation

Gas-phase methanol solvation of Cs+ : Vibrational spectroscopy and Monte Carlo simulation

Nonlinear, Nonpolar Solvation Dynamics in Water: The Roles of Electrostriction and Solvent Translation in the Breakdown of Linear Response

Ultrafast Measurements on Excited State Isomerization

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