Covariance Mapping of Ammonia Clusters:  Evidence of the Connectiveness of Clusters with Coulombic Explosion

Card, D. A.; Folmer, D. E.; Sato, Shunsuke A.; Buzza, S. A.; Castleman, A. W.

doi:10.1021/jp970414n

Cited by 39 publications

(34 citation statements)

References 54 publications

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“…During the course of investigating cluster dynamics by using highintensity femtosecond laser techniques, we discovered that with proper selection of the photoionization conditions (18,19), Coulomb explosion can be initiated in clusters at moderate fluences and in a controlled way. Using various pump-probe studies performed at selected time delays with respect to a pulsed molecular beam in which clusters were produced, and also using covariance analysis (20) to investigate the origin of observed high-charge state species, we established the critical role of clusters in effecting the Coulomb explosion phenomena (21). This led us to conceive of a way to study the course of stepwise reactions, e.g., proton transfer, by attempting to arrest the intermediates in the transfer process at selected times.…”

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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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%

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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“…second laser MPI, 34,35 and single photon ionization. 36 A high resolution spectrum for small clusters is presented in Fig.…”

Section: Distribution Of Ammonia Clusters Ionized By a Soft X-ray Lasermentioning

confidence: 99%

“…29͔͒. Ammonia clusters are investigated by EI, 30,31 MPI, 32,33 femtosecond laser, 34,35 and single photoionization 36 techniques. Like water and methanol clusters, protonated ammonia clusters somewhat surprisingly dominate its mass spectra.…”

Section: Introductionmentioning

confidence: 99%

Dynamics and fragmentation of van der Waals clusters: (H2O)n, (CH3OH)n, and (NH3)n upon ionization by a 26.5eV soft x-ray laser

Dong

Heinbuch

Rocca

et al. 2006

The Journal of Chemical Physics

102

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A tabletop soft x-ray laser is applied for the first time as a high energy photon source for chemical dynamics experiments in the study of water, methanol, and ammonia clusters through time of flight mass spectroscopy. The 26.5 eV/photon laser ͑pulse time duration of ϳ1 ns͒ is employed as a single photon ionization source for the detection of these clusters. Only a small fraction of the photon energy is deposited in the cluster for metastable dissociation of cluster ions, and most of it is removed by the ejected electron. Protonated water, methanol, and ammonia clusters dominate the cluster mass spectra. Unprotonated ammonia clusters are observed in the protonated cluster ion size range 2 ഛ n ഛ 22. The unimolecular dissociation rate constants for reactions involving loss of one neutral molecule are calculated to be ͑0.6-2.7͒ ϫ 10 4 , ͑3.6-6.0͒ ϫ 10 3 , and ͑0.8-2.0͒ ϫ 10 4 s −1 for the protonated water ͑9 ഛ n ഛ 24͒, methanol ͑5 ഛ n ഛ 10͒, and ammonia ͑5 ഛ n ഛ 18͒ clusters, respectively. The temperatures of the neutral clusters are estimated to be between 40 and 200 K for water clusters ͑10ഛ n ഛ 21͒, and 50-100 K for methanol clusters ͑6 ഛ n ഛ 10͒. Products with losses of up to five H atoms are observed in the mass spectrum of the neutral ammonia dimer. Large ammonia clusters ͑NH 3 ͒ n ͑n Ͼ 3͒ do not lose more than three H atoms in the photoionization/ photodissociation process. For all three cluster systems studied, single photon ionization with a 26.5 eV photon yields near threshold ionization. The temperature of these three cluster systems increases with increasing cluster size over the above-indicated ranges.

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“…One solution to this predicament is to perform covariance analysis, in which statistically significant relationships between various detected particles are looked for, not on an event-by event basis, but by using statistical analysis methods [30][31][32][33][34]. Covariance analysis has been shown to extract useful information even from datasets with high ionization rates per pulse.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics of XFEL-Induced Photo-Dissociation, Revealed by Ion-Ion Coincidence Measurements

et al. 2017

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X-ray free electron lasers (XFELs) providing ultrashort intense pulses of X-rays have proven to be excellent tools to investigate the dynamics of radiation-induced dissociation and charge redistribution in molecules and nanoparticles. Coincidence techniques, in particular multi-ion time-of-flight (TOF) coincident experiments, can provide detailed information on the photoabsorption, charge generation, and Coulomb explosion events. Here we review several such recent experiments performed at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan, with iodomethane, diiodomethane, and 5-iodouracil as targets. We demonstrate how to utilize the momentum-resolving capabilities of the ion TOF spectrometers to resolve and filter the coincidence data and extract various information essential in understanding the time evolution of the processes induced by the XFEL pulses.

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Covariance Mapping of Ammonia Clusters: Evidence of the Connectiveness of Clusters with Coulombic Explosion

Cited by 39 publications

References 54 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

Dynamics and fragmentation of van der Waals clusters: (H2O)n, (CH3OH)n, and (NH3)n upon ionization by a 26.5eV soft x-ray laser

Molecular Dynamics of XFEL-Induced Photo-Dissociation, Revealed by Ion-Ion Coincidence Measurements

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