Measurements of relative concentrations and velocities of small clusters (n⩽40) in expanding water vapor flows

Dreyfuss, David; Wachman, Harold Y.

doi:10.1063/1.443177

Cited by 86 publications

(12 citation statements)

References 21 publications

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“…The appearance of the ionized water clusters as protonated or deuterated species in the form of (H20),H + or (D20),D + ions observed here has already been seen in a variety of investigations [ 1,2,8]. But also the existence of unprotonated cluster ions (H20) + has been reported, which are produced by ionizing neutral (Ar)m(H20), clusters [5], by threshold photoionisation of water aggregates [29] or by using a special supersonic ion beam source [301.…”

Section: Discussionsupporting

confidence: 70%

“…The denominator of the last equation is the measured total ion signal Sk(O) of (1), so that by combining (1) and (3) with (2) finally the fragmentation probability f,k is given by fnk= SkY.k~ ~, SlcXnk.…”

Section: Size Selection and Fragmentation Analysismentioning

confidence: 99%

“…In addition, water clusters form prototypic systems for investigations of the structure and dynamics of hydrogen bonded species. Advances in molecular beam technique allow the preparation of water clusters in a wide size range either as neutral [1,2] or ionized species [3,4] in a well defined beam. Mass spectra * Present address: Laboratoire des Collisions Atomiques et Mol6culaires LCAM, Universit6 de Paris-Sud, Bat.…”

Section: Introductionmentioning

confidence: 99%

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Electron bombardment induced fragmentation of size selected neutral (D2O) n clusters

Buck¹,

Winter²

1994

Z Phys D - Atoms, Molecules and Clusters

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Abstract. The fragmentation behaviour of size selected neutral (D20)~ clusters with n<4 after ionization with 70 eV electrons is subject of this work. Size selection by scattering the cluster beam from a He target beam in combination with a quadrupole mass filter and time resolved measurements at specific laboratory angles enables us to determine the neutral precursor masses of the detected ions. The measured fragment pattern is dominated by deuterated ions of the form (D20),,_xD + with x > 1. The dimer fragmentation which leads with a probability of 62.5% to the D3 O+ ion and with 37.5% to D20 ÷ can be explained by fast intracluster ion-molecule reactions of charged monomer fragments reacting with the partner molecule. For larger clusters the fragmentation process can be rationalised by the creation of an initially highly excited D30+(DeO)x complex which is stabilized by evaporating additional monomer units with the main fragment channel (D20)D ÷ for n=3 and (D20)2D + for n=4. With increasing cluster size an increasing tendency of evaporation of more than one water monomer unit has been observed.

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Section: Discussionsupporting

confidence: 70%

Section: Size Selection and Fragmentation Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electron bombardment induced fragmentation of size selected neutral (D2O) n clusters

Buck¹,

Winter²

1994

Z Phys D - Atoms, Molecules and Clusters

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“…37 Substrate temperature during deposition varied with experiment from 77 to 140 K. Coalescence of some water molecules into gas-phase oligomers is expected to occur during beam formation. 38,39 However, the population of dimers and trimers relative to monomers reported for comparable expansion conditions is small; on the order of 1:20 and 1:100, respectively. 38,39 Following film growth, chlorodifluoromethane was deposited on ice surfaces held at 77 K utilizing a pure supersonic beam that was smaller than and centered on the water film.…”

Section: Methodsmentioning

confidence: 98%

Interaction of chlorodifluoromethane with ultrathin solid water films

Safarik

Meyer

Mullins

2001

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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The kinetics and dynamics of chlorodifluoromethane (CHF 2 Cl) adsorption on and desorption from 30-bilayer-thick amorphous solid water ͑ASW͒ and crystalline ice ͑CI͒ films were studied utilizing molecular beam techniques and thermal desorption spectroscopy. The adsorbed state and desorption kinetics of CHF 2 Cl are sensitive to the surface structure and, hence, the degree of crystallinity of ice. Chlorodifluoromethane binds more strongly to CI than ASW and desorbs at a higher temperature during thermal desorption spectroscopy ͑TDS͒, altering the spectrum line shape and allowing differentiation between the two phases. Adsorbed states and thus the TDS line shape also respond to structural changes on the ASW surface prior to the onset of crystallization. The value of the condensation coefficient ͑␣͒, a measure of CHF 2 Cl adsorption kinetics and dynamics, is high on both surfaces ͑ϳ1͒. However, a small but reproducible variation of ␣ with the phase of solid water can be used to distinguish ASW from CI. The sensitivity of CHF 2 Cl adsorption and desorption to ice surface structure can contribute information about the phase and morphology of bulk ice, provided that the structure of the surface reflects that of the bulk.

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“…Dreyfuss and Wachman 9 have reported that the minimum size for a doubly charged water cluster formed by electron impact from a neutral cluster is n =40, but the size of the neutral precursor could not be determined in their experiments.…”

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confidence: 96%

Electron-Impact Ionization of Negatively Charged Water-Cluster Ions

Beuhler

1987

Phys. Rev. Lett.

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Experimental results are presented for the electron-impact ionization of negatively charged water clusters to form singly and doubly charged positive clusters. A cluster initially containing 325 water molecules loses an average of 42 and 47 molecules, respectively, in the formation of the singly and doubly charged species with 100-V electrons. Measurement of the appearance potentials of these positively charged species yielded results consistent with ionization taking place at multiple sites within the cluster and not at a single site.PACS numbers: 36.40.+d, 34.80.Kw, 34.90.+q, 79.20.Hx Studies of the conversion of negatively charged cluster ions to positive ions by electron impact at energies less than 100 V can yield information on energy-transfer processes that lead to cluster decomposition and provide insight into ionization mechanisms operative with species having properties intermediate between molecules and bulk macroscopic systems. Electron impact of small molecules can produce doubly charged positive ions which are generally less than a few percent of total positive-ion yields. l This may be in part accounted for by the information of species which undergo Coulomb explosion. 1 In bulk systems electron impact can yield high secondary-electron yields. 2 For a MgO surface the secondary-electron yields for primary-electron energies of 1300 and 100 V are 24 and 5 electrons, 3 respectively. For electron impact of clusters, the questions of the extent of multiple ionization and degradation is of particular interest because of the increased stability of products toward Coulomb explosion compared with molecules. The purpose of this Letter is to show preliminary measurements on multiple ionization of a negatively charged water-cluster ion beam of known mass-to-charge ratio (m/e) which incorporates analysis of the m/e of the secondary products to measure mass degradation of the primary beam. In addition, the charge on these secondary ions can be uniquely determined. The results yield information on the operative ionization mechanism, and may have practical importance for the general problem of the determination of cross sections and degradation in the ionization of neutral-cluster beams.The apparatus used in this study has been described in detail in previous publications. 4 ' 5 Negatively charged water-cluster ions were grown in the expansion of a weakly ionized plasma of helium carrier gas saturated with water vapor. Cluster sizes could be controlled by variation of the arc current and nozzle geometry. 5 This primary beam was extracted from the nozzle-skimmer region and passed through an electron-impact ionizer. Depending on the polarities and voltages of the lenses after the ionization region, either primary (-) or secondary (+) ions were mass analyzed in the quadrupole mass analyzer operating at 292 kHz. Flight times of the ions in the quadrupole were approximately 100 ^usec. Beam intensities were measured with a Faraday cup. High-sensitivity detection of positive ions coupled with the ability to determine t...

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Measurements of relative concentrations and velocities of small clusters (n⩽40) in expanding water vapor flows

Cited by 86 publications

References 21 publications

Electron bombardment induced fragmentation of size selected neutral (D2O) n clusters

Electron bombardment induced fragmentation of size selected neutral (D2O) n clusters

Interaction of chlorodifluoromethane with ultrathin solid water films

Electron-Impact Ionization of Negatively Charged Water-Cluster Ions

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