Collision-induced dissociation of H 3 + ions

For collision energies between 100 and 500 eV the collision induced dissociation of H ₃ ⁺ colliding with H₂, He and Kr gas targets was measured. We obtained total cross sections and angular distributions of the charged collision fragments for the main reaction channels. H ₃ ⁺ +H₂→H⁺+2H² and H ₃ ⁺ +H₂→H ₂ ⁺ +H₂+H. An analysis of the kinetics yields that the dissociation proceeds via vibrational-rotational excitation of H ₃ ⁺ by mutually induced dipolmoments.     

Relative Anfangsbesetzungszahlen der Zustände 2p und 3d folienangeregter Wasserstoffatome

The Lyman-α radiation of fast moving hydrogen atoms excited by a thin carbon foil is measured using a channel electron multiplier with a Mg F₂ filter. The photonintensity-versus-distance curve exhibits the 2p (1.596 ns) decay followed by a cascade tail originating mainly from the 3d level (15.47 ns). The data is analyzed by a computer program using the known mean lives of the 2p, 3d, and 3s states and yields the relative initial state populationY=N _2p ⁰ N _{3 d} ⁰ which depends on the kind of incident ions (H⁺ or H₂ ⁺). For H₂ ⁺ ions, excited with a single foil, there might be a slight dependence ofY on the beam velocity, but for H⁺ ions incident on the foil, no such dependence is found.     

Messung von Lebensdauern und relativen Besetzungszahlen angeregter Zustände des Wasserstoffatoms mit der Methode der Ionenstrahlspektroskopie

H ⁺₂ ions or protons, accelerated to energies between 80 and 300 keV, are sent through a thin carbon target. Light emitted by the excited atoms moving out of the foil with a definite velocity is analyzed using interference filters and a cooled photomultiplier. Intensities of theH _α,H _β, andH _γ lines are measured as functions of the distance from the foil. The data is analyzed with a computer program, which yields (in agreement with theory) mean lives of the hydrogen atom excited states involved, and the relative initial state populations of states belonging to the same principal quantum number. There is no indication of cascading.

     

Dissociative charge exchange in collisions of 10keV H 2 + ions on H2, He,and Ar targets

The velocity distributions of H-H fragment pairs arising from dissociative collisions of 10keV H ₂ ⁺ ions incident on H₂, He, and Ar were measured using a flight-time-difference method. The H ₂ ⁺ ions were produced in an electron impact ion source at two different electron energies, at 100eV and 18eV. The influence of the electron energy on the fragment velocity distributions is studied. Conclusions are drawn on the processes which lead to the formation of neutral fragment pairs. Electron capture into the repulsive b³ Σ _u ⁺ state of H₂ plays a dominant role.     

SIMS of silicon bombarded with Sb m + cluster ions

The emission of Si _n ⁺ (n = 1–11) cluster ions and Si _n X _m ⁺ (X stands for B or Sb) polyatomic ions when bombarding a single silicon crystal with Sb _m ⁺ (m = 1–4) cluster ions with energies E ₀ = 3–12 keV is studied. Considerable nonadditive enhancement of the yield of Si _n ⁺ cluster ions and most polyatomic ions is observed when the number of atoms in the bombarding cluster ions is increased. The sensitivity enhancement factor for detecting boron impurities is as high as 50 when the cluster-SIMS-molecule technique is applied.     

A computational study of interplay between hydride bonding and cation–π interactions: H-Mg-H···X···Y triads (X = Li+, Na+, Y = C2H2, C2H4, C6H6) as model systems

In the present study, H-Mg-H···X···Y (X = Li⁺, Na⁺ and Y = C₂H₂, C₂H₄, C₆H₆) triads have been investigated at MP2/6-311++G(2d,2p) computational level to characterise cooperative effects between hydride bonding and cation–π interactions. Molecular geometries, binding energies, cooperative energies and many-body interaction energies were evaluated. The diminutive energy values in triads with Li⁺ are larger than respective values in triads with Na⁺. The electronic properties of the complexes are analysed using parameters derived from the quantum theory of atoms in molecules methodology.     

Near resonance charge transfer from a laser excited donor state

A laser induced charge transfer from Na(3p) to hydrogen-ions at different kinetic energies has been studied. An enhancement factor of about 90% in the production rate of Lyman-α radiation has been demonstrated to occur only with H⁺ and Na(3p) atoms reaction; no enhancement was observed with either H ₂ ⁺ or H ₃ ⁺ ions. Absolute cross-section for the production of Lyman-α radiation during the collision of H⁺, H ₂ ⁺ and H ₃ ⁺ ions and Na(3p) and Na(3s) atoms have been measured in the energy range 1–600eV. The charge exchange reactions involving hydrogen-ions and Na(3p) atoms created by two different methods have also been compared.     

Weak contributions to angular asymmetries ine + e − annihilation

We study the energy and polarization dependence of angular asymmetries ine ^? e ⁺→ψ,Z ⁰→f \(\bar f\) (f=lepton or quark). Through the fragmentation of the quarks the corresponding asymmetries are obtained for the jet axis ine ^? e ⁺→ψ,Z ⁰→(Σq \(\bar q\) )→2 jets, and for inclusively produced hadronsh(h=π⁺,K ⁺ and π⁺ +K ⁺) ine ^? e ⁺→ψ,Z ⁰→(Σq \(\bar q\) )→(h+X)_2jet. In the Weinberg-Salam model these asymmetries come out big enough to show up already at upper PETRA and PEP energies.     

The Hammond postulate: A quantitative interpretation

The Hammond postulate is considered in terms of the model of intersecting parabolas. It is shown that, in radical detachment reactions of the type X _f ^· + HX _i → X _f H + X _i ^· with a symmetrical reaction center X _i …H…X _f , the H atom in the transition state is equidistant from the X _i and X _f atoms if the enthalpy of the reaction ΔH = 0. The X _i …H distance increases and the X _f …H distance decreases linearly as ΔH grows. The dependence remains linear over the range ΔH _min ≤ ΔH ≤ H _max. The same result was obtained in quantum-chemical calculations for reactions of the type R _f ^· + R _i H. In reactions of the type X^· + HY → XH + Y^· with an asymmetric reaction center X…H…Y, the X…H and Y…H interatomic distances in the transition state at ΔH = 0 depend on the force constants and lengths of the X-H and Y-H bonds. The Y…H distance increases and the X…H distance decreases linearly as ΔH grows. A similar picture is observed in the model of intersecting Morse curves, where the dependence of interatomic distances on ΔH in the transition state is nonlinear. Equations describing interatomic distances in the transition state as functions of the enthalpy of the reaction are presented.     

Calculation of molecular constants for the X 1Σ g + , A 1Σ u + , B 1Πu, and a 3Σ u + electronic states of 39K2

The molecular constants are calculated for the X ¹Σ _g ⁺ , A ¹Σ _u ⁺ , B ¹Π_u, and a ³Σ _u ⁺ and electronic states of a potassium dimer. The wave functions and vibrational energies necessary for calculating the molecular constants are determined by solving the radial wave equation with the use of potential energy curves constructed by the semiempirical method. The vibrational terms, the rotational constants, and the centrifugal distortion constants calculated from the potential curves are compared with those determined from the experimental data.     

Studies on the full vibrational energy spectra for some electronic states of diatomic molecular ions XY+

The first accurate studies on the vibrational spectroscopic constants and the corresponding full vibrational energy spectra of some electronic states of diatomic molecular ions XY⁺ were performed using algebraic method(AM). The AM is applied on the X¹Σ⁺ state of BeH⁺, the X²Σ⁺ state of CO⁺, the X²Π_g state of F ₂ ⁺ , the A²Π_u state of O ₂ ⁺ and the X²Σ _g ⁺ state of Li ₂ ⁺ . The results show that AM can generate accurate vibrational spectroscopic constants as well as accurate full vibrational energy spectra by using some accurate experimental vibrational energies, and that the AM vibrational energies are better than other theoretical data. __________ Translated from Chinese Journal of Atomic and Molecular Physics, 2005, 22 (4) (in Chinese)     

Radiative capture of deuterons in154Sm and238U

Angular — and velocity — distributions of electrons emitted near zero degree from projectile ions (H⁺, H ₂ ⁺ , H ₃ ⁺ , He⁺, He⁺⁺ at 1.7 MeV/u) traversing solid carbon foils (2 to 20) μg/cm²) have been measured. The data give clear evidence of production mechanisms which go beyond those reported elsewhere.     

Angular distributions of dileptons in polarized hadronic collisions: Test of electroweak gauge models

The angular distributions of high-mass dileptons with large transverse momentum produced in longitudinally polarized hadronic collisions, hadron +hadron→(γ^*,Z ₁ ⁰ ,Z ₂ ⁰ , ...)+X→l ⁺ l ^?+X, are calculated in the QCD lowest order. The formulas presented in general form, are applicable to any gauge model of underlying electroweak interactions. Numerical results are obtained for the angular distributions in \(\bar p\) p-collisions at \(\sqrt s = 540GeV\) for the Weinberg-Salam,SU(2)×U(1)×U(1)′ andSU(2)×SU(2)′×U(1) models. Clearly distinguishable signals are revealed.     

Stoßdissoziation von H 2 + - und D 2 + -Ionen

The angular and energy distribution of protons produced by collision-induced dissociations of H ₂ ⁺ ions with energies of 10 and 20 keV were measured in a parabola spectrograph. From these measurements the velocity distribution of the protons in the center of mass system of the H ₂ ⁺ ion can be calculated. This gives information about the type, the abundance, and the anisotropy of the processes involved. The most frequent transitions leading to dissociations are the excitation of the 2pσ_u state, the ionisation of the H ₂ ⁺ ion, the transition into the vibrational continuum, and the electron capture into the 1³ σ _u ⁺ state of the hydrogen. It is shown that the cross section for an electronic transition depends on the velocity of the ion, the distance of the nuclei in the ion, the angle between the internuclear axis and the direction of the primary ion beam, and the excitation energy of the target. The fraction of protons produced by vibrational excitation increases with increasing atomic number of the target. Concerning electronic transitions D ₂ ⁺ ions equal H ₂ ⁺ ions of the same velocity.     

Energy spectra and energy correlations in the decayH→ZZ→μ+μ−μ+μ−

It is shown that in the sequential decay $H \to ZZ \to (f_1 \bar f_1 ) + (f_2 \bar f_2 )$ , the energy distribution of the final state particles provides a simple and powerful test of theHZZ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame ofH, is predicted to be dΓ/dx～1+β⁴?2(x?1)², with $\beta = \sqrt {1 - 4m_Z^2 /m_H^2 } $ and 1?β≤x=4E/m _H ≤1+β. By contrast, the spectrum for a pseudoscalar Higgs is dΓ/dx～β²+(x?1)². There are characteristic energy correlations betweenf ₁ andf ₂ and betweenf ₁ andf ₂. These considerations are applied to the “gold-plated” reactionH→ZZ→μ⁺μ^?μ⁺μ^?, including possible effects ofCP-violation in theHZZ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H \to W^ + W^ - \to l^ + v_l l^ - \bar v_l $ .     

An efficient basis set representation for calculating electrons in molecules

ABSTRACT

The method of McCurdy, Baertschy, and Rescigno, J. Phys. B, 37, R137 (2004) [1 C.W. McCurdy, M. Baertschy, and T.N. Rescigno, J. Phys. B 37, R137 (2004).[Crossref], [Web of Science ®] , [Google Scholar]] is generalised to obtain a straightforward, surprisingly accurate, and scalable numerical representation for calculating the electronic wave functions of molecules. It uses a basis set of product sinc functions arrayed on a Cartesian grid, and yields 1 kcal/mol precision for valence transition energies with a grid resolution of approximately 0.1 bohr. The Coulomb matrix elements are replaced with matrix elements obtained from the kinetic energy operator. A resolution-of-the-identity approximation renders the primitive one- and two-electron matrix elements diagonal; in other words, the Coulomb operator is local with respect to the grid indices. The calculation of contracted two-electron matrix elements among orbitals requires only O(Nlog?(N)) multiplication operations, not O(N⁴), where N is the number of basis functions; N = n³ on cubic grids. The representation not only is numerically expedient, but also produces energies and properties superior to those calculated variationally. Absolute energies, absorption cross sections, transition energies, and ionisation potentials are reported for 1- (He⁺, H⁺₂), 2- (H₂, He), 10- (CH₄), and 56-electron (C₈H₈) systems.     

Molecular adsorbate detection using hyperthermal Cs+ surface scattering: chemisorbed water on Si(111)

Cs⁺ ion beams are scattered from an Si(111) surface chemisorbed with water. Scattering of Cs⁺ ions from the surface at the incidence energies of 10–;15 eV gives rise to reaction products CsOH⁺, CsOH⁺₂ and CsSiO⁺. We interpret that these cluster ions are formed by desorption of X (X = OH, H₂O and SiO), followed by Cs⁺X association and energy quenching near the surface. The Cs⁺ scattering method has potential advantages for adsorbate detection over desorption techniques, in particular for identification of molecular and thermally unstable species.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

Features of the variation in reflection spectra of the F4MB/Al coating under bombardment by H+, H 2 + and H 3 + ions

Variations of reflection spectra for the F4MB/Al coating, based on fluoroplastic film, occurring under bombardment by H⁺, H ₂ ⁺ , and H ₃ ⁺ , ions with energy 15 keV are investigated. It is established that the variations in the reflection spectra and integrated absorption coefficient are not proportional to the mass of the hydrogen ion and obey the different regularities depending on the energy of the absorption band.     

Measuring theWW γ vertex in the processep→γϑX

We present a detailed analysis of the processep→γ?X as a means of studying the gauge structure of theWWγ vertex. We find that the differential cross section of highp _T photons offers a sensitive measure of anomalousWWγ couplings. At HERA \((\sqrt s = 314GeV)\) , after several years of running, theWWγ vertex can be measured to δκ_γ ? _?2.0 ^+2.9 and δλ_γ ? _?2.5 ^+3.0 (95% C.L.). Which offers an improvement over existing constraints from direct measurements using associatedWγ production in \(\bar pp\) collisions but is less sensitive than the competing process at HERA,ep→eWX. For a higher energyep collider, LEP-LHC \((\sqrt s = 1.3TeV)\) , theWWγ vertex can be measured to δδκ_γ ? ± 0.4 and δλκ_γ ? ± 0.1 at 95%C.L. which is more sensitive to λ_γ than the processe ⁺ e ^?→W ⁺ W ^? at the LEP200e ⁺ e ^? collider and is comparable to the LEP200 sensitivity to κ_γ. These values are also roughly comparable to the competing processep→eWX at LEP-LHC and to what is expected from associated γW production at the LHC and SSC for κ_γ but they are about half as sensitive to λ_γ as the LHC and SSC.