Large Differences in Surface Ionization Efficiencies between K and its Halides on the Contaminated Surface of a Pt Alloy (8% W) Wire

Touw, T. R.; Trischka, J. W.

doi:10.1063/1.1729279

Cited by 70 publications

(7 citation statements)

References 3 publications

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“…The total scattering (M + MX) was detected with a Re surface ionization filament operated at -1700 K, the reactive scattering (M atoms) with a Pt -8% W alloy filament operated at -1300 K and preconditioned by heating at -1600 K for a few minutes in methane at lo4 Torr to render the filament insensitive to alkali halides (28). Both filaments were ribbons, 0.03 mm thick and 0.76 mm wide.…”

Section: Methodsmentioning

confidence: 99%

Molecular beam kinetics: reactions of H and D atoms with alkali halides

Siska¹,

Herschbach²

1994

Can. J. Chem.

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Angular distributions of alkali atoms produced in crossed-beam reactions of H and D atoms (at -2800 K) with KF, CsF, KC1, CsC1, and KBr (at -1100-1200 K) have been measured. For these systems, the reaction exoergicity varies from ADo -17 kcall mol for H + KF to -4 kcaVmol for H + KBr; the thermal distribution of the reactant energy peaks near 12 kcallmol with E -9 kcaYmo1 in relative translation and W -3 kcallmol in vibration and rotation of the alkali halide. Kinematic analysis of the data is canied out by means of a least-squares procedure that includes averaging over the parent beam velocity distributions. The main results are (1) The reaction cross sections Q, vary from -1 to 30 A ' . The magnitude correlates with ADO and with the identity of the halogen for a given alkali, decreasing as F -+ C1+ Br. For a given halogen, Q, is 2-3 times larger for the Cs reaction than for K and about 2 times larger for D than for H. (2) Temperature-dependence measurements for the CsCl case indicate the activation energy (in excess of endoergicity) is near zero. (3) The preferred direction of the reactively scattered alkali atoms with respect to the incident alkali halide varies with the halogen, from mainly forward for the KBr reaction to more sideways for the KF and CsF reactions. (4) The partitioning of energy between product translation E' (M relative to HX) and internal excitation W' (vibration and rotation of HX) can only be roughly estimated; our data are consistent with E' -Wand W' -E + ADo but a definitive analysis will require product velocity distributions or spectra. These results are discussed in terms of a dynamical model akin to Polanyi's DIPR model. This postulates that the motion of H or D is approximately separable from that of the heavier atoms and the preferred reaction geometry corresponds to a triangular H-X-M complex. [Traduit par la rtdaction]

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Section: Methodsmentioning

confidence: 99%

Molecular beam kinetics: reactions of H and D atoms with alkali halides

Siska¹,

Herschbach²

1994

Can. J. Chem.

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“…Scattered molecules are detected by a surface ionization detector [1]. The W filament heated to ~ 1600~ ionizes alkali dimers, atoms and reactively scattered alkali halide ; the Pt/W filament at ,-, 1000~ after treatment with methane [17,18], has a greatly decreased ionization efficiency for alkali Reactive scattering of alkaK dimers 129 halides. The potassium dimer beam intensity ~2.5xl0-SA is attenuated ~5 per cent by the cross beam, giving an alkali halide product intensity ~,,4x 10 -13 A corresponding to ,,-4x l0 s molecules cm -z s -1 at the peak of the product distribution.…”

Section: Experimental Methodsmentioning

confidence: 99%

Reactive scattering of alkali dimers: K₂+ Br₂, ICl, IBr, BrCN

1972

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Angular distribution measurements of KX or KCN reactive scattering of a potassium dimer Ks beam by cross beam molecules Br2, IC1, IBr and BrCN are reported. The magnitude of the total reaction cross-sections indicates that the entrance valley is dominated by an electron jump. Forward peaking of the centre of mass differential cross sections suggests that the Ks + ion dissociates more slowly than the XY-ion in large impact parameter collisions. The predominant reaction path yields a potassium halide (or cyanide) and potassium atom, KX+ K+Y. These features are rendered plausible in terms of the electronic structure of the potential surface. 1. INTRODUCTION Considerable insight has been gained into the dynamics of chemical reactions through the techniques of molecular beam kinetics. Direct mechanisms with rebound [1], intermediate [2] and stripping [3-5] angular distributions have been exhibited by the reactions of alkali atoms with alkyl iodide, polyhalide and halogen molecules. Long-lived complex mechanisms have been observed in the reactions of alkali atoms with alkali halides [6] ; short-lived complexes in halogen atomhalogen molecule [7, 8] and alkali atom-thallium halide reactions [9]. However, even this prodigious versatility represents only the reactions of atoms with diatomic molecules, i.e. three centre metathetical reactions. wThe next stage of mechanistic complexity arises with four centre reactions. The reactions of alkali atoms with triatomic molecules [10], proceeding by a stripping mechanism do demonstrate some effects of the internal motion of the triatomic molecule. However, the full dyamical complexity of four centre reactions is to be anticipated in diatomic molecule-diatomic molecule reactions. In this category only the alkali halide-alkali halide exchange reaction [11] has been studied. Even here the limited reaction exothermicity results in a long-lived complex mechanism, so that potential dynamical complexities are ' washed out ' Thus, considerable interest attaches to studies of diatomic-diatomic four centre reactions proceeding by a direct mechanism. With this end in view, we have studied the reactions of alkali dimers with a range of cross beam molecules. A preliminary account [12] of the reactions of potassium dimers with halogen molecules has already been reported.

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“…This is also not a very satisfying explanation, but such effects are known to occur at high temperatures. For example, the work function of platinum-tungsten alloy is dependent on exposure to oxidizing or reducing atmospheres [19]. The work function could in turn affect the heterogeneous reactivity.…”

Section: C1-hcl Wallmentioning

confidence: 99%

Chlorine atom and ClO wall reaction products

Martin

Wren

Wun

1979

Int J of Chemical Kinetics

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The products of the heterogeneous reactions of chlorine atoms and chlorine oxide radicals with acid coated Pyrex walls have been directly determined for the first time. Contrary to the usual assumption that chlorine atoms recombine to form Clz, we find that the major product is HCl, with small amounts of perchlorate also formed. Similarly, C10 radicals form HC1 rather than Clz. The source of hydrogen for these reactions is probably the water always found in this type of vacuum system. These results may change the interpretation of flow tube experiments with chlorine atoms. Application to the H + HC1 reaction is discussed as an example.

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Large Differences in Surface Ionization Efficiencies between K and its Halides on the Contaminated Surface of a Pt Alloy (8% W) Wire

Cited by 70 publications

References 3 publications

Molecular beam kinetics: reactions of H and D atoms with alkali halides

Molecular beam kinetics: reactions of H and D atoms with alkali halides

Reactive scattering of alkali dimers: K₂+ Br₂, ICl, IBr, BrCN

Chlorine atom and ClO wall reaction products

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Large Differences in Surface Ionization Efficiencies between K and its Halides on the Contaminated Surface of a Pt Alloy (8% W) Wire

Cited by 70 publications

References 3 publications

Molecular beam kinetics: reactions of H and D atoms with alkali halides

Molecular beam kinetics: reactions of H and D atoms with alkali halides

Reactive scattering of alkali dimers: K2+ Br2, ICl, IBr, BrCN

Chlorine atom and ClO wall reaction products

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Reactive scattering of alkali dimers: K₂+ Br₂, ICl, IBr, BrCN