Fragmentation of transient water anions following low-energy electron capture by H<sub>2</sub>O/D<sub>2</sub>O

Fedor, Juraj; Cicman, P.; Coupier, B.; Feil, S.; Winkler, M.; Głuch, K.; Husarik, J; Jaksch, D.; Farizon, B.; Mason, Nigel J.; Scheier, P.; Märk, T.D.

doi:10.1088/0953-4075/39/18/022

Cited by 69 publications

(85 citation statements)

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“…Dimethylacetylene (liquid at standard laboratory conditions) was kept in a glass tube immersed in ethylene glycol cooled down to −22 • C. Keeping the samples at low temperatures increased the purity of the sample, since it lowered the partial vapor pressure of impurities with substantially different volatilities. This concerns mainly water, which upon DEA yields H − anions at similar energies as the present samples [27].…”

Section: Methodssupporting

confidence: 65%

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

2012

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We have measured absolute dissociative electron attachment (DEA) cross sections in methylacetylene (propyne, C 3 H 4 ) and dimethylacetylene (but-2-yne, C 4 H 6 ). The main feature in the low-energy DEA spectrum is a π * shape resonance giving rise to fragments at 3.4 eV in C 3 H 4 and 4.0 eV in C 4 H 6 . The process C 3 H 4 + e → C 3 H − 3 + H proceeds via abstraction of the acetylenic hydrogen which is mediated by effective vibronic coupling. The abstraction of methyl group hydrogen, which does not require symmetry lowering of the transient negative ion, was not observed; the spatial separation of the bond from the resonance decreases the cross section dramatically. The presence of the methyl group further influences the DEA cross sections via change of the resonance's position and via blocking one or both of the DEA active sites in acetylene. No cleavage of the C-methyl bond has been observed, and reasons for this effect are discussed. Additionally, several higher-lying resonances (6 to 15 eV) leading to production of an H − fragment were observed and assigned.

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Section: Methodssupporting

confidence: 65%

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

2012

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“…The three-body breakup threshold is 8.04eV for production of H + H + O − , and 8.75eV for H − + H + O; the onsets for the experimental peaks for O − and H − via 2 A 1 are approximately 7.9 and 7.5eV, respectively [10]. Our potential energy surfaces, however, do not distinguish between the three-body asymptotes.…”

mentioning

confidence: 56%

“…Our final results for O − production in DEA to the water molecule are summarized and compared with the recent results of Fedor et al [10] in Fig.3. The 2 B 1 result is unchanged from our zero result [19]; O − is the most minor channel ( 1 40 branching ratio) in this system and represents the only qualitative failure of our treatment.…”

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confidence: 74%

“…is a resonant process that involves the capture of a free electron into a transient negative ion state which subsequently dissociates to produce neutral and ionic fragments. Previous experimental [1][2][3][4][5][6][7][8][9][10] and theoretical studies [11][12][13][14][15][16][17][18][19] [9] observed the opening of the lower three-body channel, as discerned through the kinetic energy distribution of the O − fragment. However, because of the large O atom/H 2 mass ratio, such a measurement is difficult and a quantitative experimental determination of the final-state branching ratios among the two-and three-body breakup channels has yet to be published.…”

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confidence: 99%

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Three-body breakup in dissociative electron attachment to the water molecule

2008

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We report the results of ab initio calculations on dissociative electron attachment (DEA) to water that demonstrate the importance of including three-body breakup in the dissociation dynamics. While three-body breakup is ubiquitous in the analogous process of dissociative recombination, its importance in low-energy dissociative electron attachment to a polyatomic target has not previously been quantified. Our calculations, along with our earlier studies of DEA into two-body channels, indicate that three-body breakup is a major component of the observed O − cross section. The local complex potential model provides a generally accurate picture of the experimentally observed features in this system, reproducing some quantitatively, others qualitatively, and one not at all.PACS numbers: 03.65. Nk, 34.80.Ht Dissociative electron attachment (DEA) to the water molecule, [9] observed the opening of the lower three-body channel, as discerned through the kinetic energy distribution of the O − fragment. However, because of the large O atom/H 2 mass ratio, such a measurement is difficult and a quantitative experimental determination of the final-state branching ratios among the two-and three-body breakup channels has yet to be published.There is strong reason to believe that three-body breakup is important for describing DEA leading to O − production. In particular, examination of the shape of the 2 A 1 surface suggests that three-body breakup may be the key to describing O − production via this resonance. The 2 A 1 (1 2 A ′ ) electronic surrface slopes downward toward linear H-O-H geometry and is dissociative along the OH bonds. It provides a path for symmetric dissociation of the OH bonds to produce O − + H + H, but also slopes downward toward the H − + OH asymptotes. Similarly, the 2 B 2 diabatic surface, which equals the 2 B 2 adiabatic surface for C 2v geometries, provides a path toward symmetric dissociation through the conical intersection with the 2 A 1 state. Symmetric dissociation of the 2 B 2 state from the equilibrium geometry of the neutral leads to the O − + H + H three-body asymptote.Our methodology is very similar to that used in our previous calculations, so we provide only a brief summary

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“…Although water clusters have positive electron affinities [70], the electron affinity of an isolated water molecule is either very small or zero [71]. Electron attachment to an isolated water molecule results in spontaneous dissociation to form predominantly H Ϫ with minor abundances of O Ϫ and OH Ϫ also observed [72]. With increasing incident electron energies, some internal vibration modes can be excited, but the majority of the dissociation energy is carried away by the fragments in the form of kinetic energy [73].…”

Section: Evidence For Nonergodic Dissociationmentioning

confidence: 99%

Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry

Leib

Donald

Bush

et al. 2007

J. Am. Soc. Mass Spectrom.

118

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Hydrated divalent magnesium and calcium clusters are used as nanocalorimeters to measure the internal energy deposited into size-selected clusters upon capture of a thermally generated electron. The infrared radiation emitted from the cell and vacuum chamber surfaces as well as from the heated cathode results in some activation of these clusters, but this activation is minimal. No measurable excitation due to inelastic collisions occurs with the low-energy electrons used under these conditions. Two different dissociation pathways are observed for the divalent clusters that capture an electron: loss of water molecules (Pathway I) and loss of an H atom and water molecules (Pathway II). For Ca(H 2 O) n 2ϩ , Pathway I occurs exclusively for n Ն 30 whereas Pathway II occurs exclusively for n Յ 22 with a sharp transition in the branching ratio for these two processes that occurs for n Ϸ 24. The number of water molecules lost by both pathways increases with increasing cluster size reaching a broad maximum between n ϭ 23 and 32, and then decreases for larger clusters. From the number of water molecules that are lost from the reduced cluster, the average and maximum possible internal energy is determined to be ϳ4.4 and 5.2 eV, respectively, for Ca(. This value is approximately the same as the calculated ionization energies of M(H 2 O) n ϩ , M ϭ Mg and Ca, for large n indicating that the vast majority of the recombination energy is partitioned into internal modes of the ion and that the dissociation of these ions is statistical. For smaller clusters, estimates of the dissociation energies for the loss of H and of water molecules are obtained from theory. For Mg(H 2 O) n 2ϩ , n ϭ 4 -6, the average internal energy deposition is estimated to be 4.2-4.6 eV. The maximum possible energy deposited into the n ϭ 5 cluster is Ͻ7.1 eV, which is significantly less than the calculated recombination energy for this cluster. There does not appear to be a significant trend in the internal energy deposition with cluster size whereas the recombination energy is calculated to increase significantly for clusters with fewer than 10 water molecules. These, and other results, indicate that the dissociation of these smaller clusters is nonergodic. . The effectiveness of the bottom-up method for complex samples can be enhanced by using multidimensional separations. Clemmer and coworkers elegantly demonstrated that combining on-line liquid chromatography (LC) with ion mobility spectrometry and MS can greatly improve separations without increasing analysis times over LC/MS alone [2][3][4]. In contrast, the "top-down" approach to protein characterization has the advantage that de novo sequencing, including the identification and structural localization of labile posttranslational modifications, can be done directly on protein mixtures without proteolysis [5,6]. This top-down approach has greatly benefited from the development of electron capture dissociation (ECD), a method pioneered by McLafferty and coworkers [6][7][8][9]. In a typical ECD experim...

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Fragmentation of transient water anions following low-energy electron capture by H₂O/D₂O

Cited by 69 publications

References 28 publications

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

Three-body breakup in dissociative electron attachment to the water molecule

Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry

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Fragmentation of transient water anions following low-energy electron capture by H2O/D2O

Cited by 69 publications

References 28 publications

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

Dissociative electron attachment to methylacetylene and dimethylacetylene: Symmetry versus proximity

Three-body breakup in dissociative electron attachment to the water molecule

Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry

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Fragmentation of transient water anions following low-energy electron capture by H₂O/D₂O