Molecular Dynamics Simulation of Coulomb Explosion Processes

Poth, L.; Castleman, A. W.

doi:10.1021/jp980311k

Cited by 30 publications

(21 citation statements)

References 33 publications

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“…Experiment, as well as theory, indicates that the formation of ions in a femtosecond laser pulse (22) and the concomitant Coulomb explosion phenomenon (21) are completed on a very short time scale (ref. 23; unpublished calculations were performed to determine the separation time between two model 7-Aza monomers yielding times less than 25 fs), lending promise that the Coulomb explosion imaging method could be used in ''viewing'' intermediates at selected times during the course of a reaction (11,24). We have successfully used this method to follow the course of reactions in 7-Aza dimers and to detect the reaction intermediate as well.…”

Section: Experimental Methods and Conceptsmentioning

confidence: 99%

“…It was concluded that the rise and fall of the 119-atomic mass unit (amu) species, with respect to the 118-amu species, represented the formation of an intermediate species, followed by subsequent tautomer formation in accordance with the temporal dependence of the Coulomb explosion-generated mass fragments. Calculations suggest that the time scale during which the molecular centers separate by Coulomb explosion, and thereby prevent further transfer of the protons, is on the order of 25 fs, thus making this method a useful technique for interrogating ultrafast reaction intermediates (23). The transient behavior of the protonated 7-Aza monomer arising from the Coulomb explosion event (mass 119 amu) can be attributed only to a stepwise transfer process, with an associated minimal contribution to mass 119 due to the isotopic distributions of the constituent atoms.…”

Section: Experimental Methods and Conceptsmentioning

confidence: 99%

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Femtosecond cluster studies of the solvated 7-azaindole excited state double-proton transfer

Folmer

Wisniewski

Hurley

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

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Presented here are femtosecond pump-probe studies on the watersolvated 7-azaindole dimer, a model DNA base pair. In particular, studies are presented that further elucidate the nature of the reactive and nonreactive dimers and also provide new insights establishing that the excited state double-proton transfer in the dimer occurs in a stepwise rather than a concerted manner. A major question addressed is whether the incorporation of a water molecule with the dimer results in the formation of species that are unable to undergo excited state double-proton transfer, as suggested by a recent study reported in the literature [Nakajima, A., Hirano, M., Hasumi, R., Kaya, K., Watanabe, H., Carter, C. C., Williamson, J. M. & Miller, T. (1997) J. Phys. Chem. 101, 392-398]. In contrast to this earlier work, our present findings reveal that both reactive and nonreactive dimers can coexist in the molecular beam under the same experimental conditions and definitively show that the clustering of water does not induce the formation of the nonreactive dimer. Rather, when present with a species already determined to be a nonreactive dimer, the addition of water can actually facilitate the occurrence of the proton transfer reaction. Furthermore, on attaining a critical hydration number, the data for the nonreactive dimer suggest a solvation-induced conformational structure change leading to proton transfer on the photoexcited half of the 7-azaindole dimer. C luster science studies have long been utilized to yield unique perspectives of microscopic properties related to the bulk condensed phase (1). This approach involves the investigation of a broad spectrum of clusters ranging from isolated species to the study of fully solvated species, thus illustrating the progression from the gas phase to the condensed phase. In reference to our specific experiments as an example, we have been able to study the excited state double-proton transfer (ESDPT) of the 7-azaindole (7-Aza) dimer under conditions ranging from an isolated dimer to a state of solvation where the hydrogen-bonded dimer is clustered with as many as nine water molecules. As the number of water molecules on the nonreactive dimer increases, we begin to see evidence that the dimer molecule is behaving more as it would in a fully solvated condensed-phase environment. In support of these findings, it has been reported that clusters with as little as six waters begin to show liquid-like properties (2-4).The model DNA base pair 7-Aza has proven to be an interesting and enlightening species for study in both the gas and condensed phases. Of utmost interest is the double-proton transfer that the 7-Aza dimer undergoes on excitation to the S 1 state. This ESDPT was first observed in solution by Kasha and coworkers (5). Later, Kaya and coworkers performed extensive supersonic jet spectroscopic studies on the 7-Aza monomer, dimer, and solvated forms of these species (6-9). The first direct determination of the rates of the double-proton transfer was made in the gas phase by Zewail and c...

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Section: Experimental Methods and Conceptsmentioning

confidence: 99%

Section: Experimental Methods and Conceptsmentioning

confidence: 99%

Femtosecond cluster studies of the solvated 7-azaindole excited state double-proton transfer

Folmer

Wisniewski

Hurley

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

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“…High-flux femtosecond laser pulses provide short bursts of light up to 10 15 W͞cm 2 , leading to the delivery of many photons to a cluster and an almost instantaneous loss of many electrons, in some cases all of the valence electrons (14,(22)(23)(24)(25). These initially ionized free electrons can further ionize the inner-shell electrons of the atomic constituents of the cluster through intracluster inelastic electron-atom collisions.…”

mentioning

confidence: 99%

“…These initially ionized free electrons can further ionize the inner-shell electrons of the atomic constituents of the cluster through intracluster inelastic electron-atom collisions. During the photon absorption and subsequent ionization processes, there is little time for nuclear motion (23)(24)(25). The highly charged atomic ions of the cluster are formed in very close proximity, and hence the system thereafter rapidly explodes because of the coulomb repulsion from like charges, releasing atomic ions with high kinetic energies (21,26,27).…”

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confidence: 99%

Clusters: A bridge across the disciplines of physics and chemistry

Jena

Castleman

2006

Proc. Natl. Acad. Sci. U.S.A.

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228

161

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“…This leads to a build-up of positive charge in the cluster and subsequent Coulomb explosion. 15 In addition, it is well-established 16-18 that certain molecules and clusters exhibit an enhancement in ionization. This enhancement results from collective electron processes in which the laser intensity requirement for the onset of ion signal for a particular atomic charge state is lower than its corresponding sequential ionization potential (IP).…”

Section: Introductionmentioning

confidence: 99%

Ionization enhancement in silicon clusters and germanium atoms in the presence of zirconium

Ross

Castleman

2012

The Journal of Chemical Physics

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Molecules/clusters have been shown to undergo an enhancement in ionization under ultrafast laser pulses. This enhancement results in the lowering of the laser intensity required to observe ion signal from higher atomic charge states resulting from Coulomb explosion of clusters. Here, we explore the effect of using an early-group transition metal as an electron source in the formation of small silicon clusters on the observed enhancement in ionization. Intensity selective scanning is used to measure the onset of ion signal for the atomic charge states of silicon, germanium, zirconium, and oxygen. Additionally, the kinetic energy released values for the resulting high charge states of silicon are measured and compared to those previously observed using a copper electron source. A significant increase in ionization enhancement is observed upon using zirconium metal, despite a decrease in cluster size. Germanium metal with zirconium is studied for comparison and shows a larger enhancement in ion signal than silicon, indicating that atomic mass may be significant.

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Molecular Dynamics Simulation of Coulomb Explosion Processes

Cited by 30 publications

References 33 publications

Femtosecond cluster studies of the solvated 7-azaindole excited state double-proton transfer

Femtosecond cluster studies of the solvated 7-azaindole excited state double-proton transfer

Clusters: A bridge across the disciplines of physics and chemistry

Ionization enhancement in silicon clusters and germanium atoms in the presence of zirconium

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