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Adsorption and thermal dehydrogenation of ammonia on Ru(112¯1) (2001)

Jacobi, K. ; Wang, Y. ; Fan, C. Y. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 115 (2001), S. 4306-4313

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Adsorption and thermal dehydrogenation of NH3, adsorbed at 80 K on the open Ru(112¯1) surface, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). For the NH3 monolayer, a strong dipole-active mode is found at 15 meV which is newly assigned to Tz, the frustrated-translation mode perpendicular to the surface of NH3 bonding with the nitrogen atom to the Ru surface. Increasing the temperature, 70% of NH3 desorbs before a channel for dehydrogenation opens at about 280 K. The remaining 30% decomposes completely during further warming to 470 K. The dehydrogenation of NH3 gives rise to four peaks in the H2 TDS which are assigned to desorption of coadsorbed hydrogen at 220 K and three dehydrogenation reaction steps at 320, 360, and 420 K in accordance with HREELS. The reaction intermediates NH2 and NH are identified through HREELS. In a new interpretation NH2 is characterized by intense modes at 163 meV (rocking) and at 189 meV (scissoring). Using a maximum entropy algorithm six frequencies for ν(Ru–N) were resolved at 46, 50, 58, 61, 69, and 75 meV. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1390523

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2

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The oxidation of CO on RuO2(110) at room temperature (2001)

Fan, C. Y. ; Wang, J. ; Jacobi, K. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 114 (2001), S. 10058-10062

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: RuO2(110) surfaces were prepared by exposing Ru(0001) to 107 L of O2 at 700 K. Postexposure of O2 at 300 K resulted in an additional oxygen species (O-cus) adsorbed on coordinatively unsaturated Ru atoms (Ru-cus). The surface was then exposed to CO at 300 K and studied by thermal desorption spectroscopy (TDS) and high-resolution electron energy loss spectroscopy (HREELS). It is demonstrated that CO is oxidized at 300 K through reaction with both the O-cus as well as with surface O-atoms held in bridge positions (O-bridge). Although—at room temperature—CO adsorbs intermediately on the Ru-cus atoms, it is stable only at the Ru atoms underneath the O-bridge after the latter has been reacted off. At room temperature only surface oxygen takes part in the CO oxidation and the oxygen-depleted surface can be restored by O2 exposure, so that under steady-state flow conditions an oxygen-deficient surface will exist whose stoichiometry will be determined by the ratio of partial pressures. © 2001 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.1350817

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3

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Neutral gas measurements of comet Halley from Vega 1 (1986)

Keppler, E. ; Afonin, V. V. ; Curtis, C. C. ; [et al.]

[s.l.] : Nature Publishing Group

Nature 321 (1986), S. 273-274

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The ING instrument comprises two independent gas detection systems, pointed in the direction of the spacecraft-comet relative velocity1. We report here results obtained by the field ionization system (FIS), which uses a high-gradient electric field to ionize incoming atoms or molecules, while ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/321273a0

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4

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The composition of heavy ions in solar energetic particle events (1984)

Fan, C. Y. ; Gloeckler, G. ; Hovestadt, D.

Springer

Space science reviews 38 (1984), S. 143-178

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ISSN: 1572-9672

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract We review recent advances in determining the elemental, charge-state, and isotopic composition of ≲ 1 to ≲ 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations. The composition within individual SEP events may vary both with time and energy, and will in general be different from that in other SEP events. Average values of relative abundances measured in a large number of SEP events, however, are found to be roughly energy independent in the ∼ 1 to ∼ 20 MeV per nucleon range, and show a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion. Direct measurements of the charge states of SEPs have revealed the surprisingly common presence of energetic He+ along with heavy ions with typically coronal ionization states. High-resolution measurements of isotopic abundance ratios in a small number of SEP events show these to be consistent with the universal composition except for the puzzling overabundance of the SEP 22Ne/20Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of 3He-rich, heavy-ion rich and carbon-poor SEP events, along with direct measurements of the ionization states of SEPs provide essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production. It is concluded that SEP acceleration is a two-step process, beginning with plasma-wave heating of the ambient plasma in the lower corona, which may include pockets of cold material, and followed by acceleration to the observed energies by either flare-generated coronal shocks or Fermi-type processes in the corona. Interplanetary propagation as well as acceleration by interplanetary propagating shock will often further modify the composition of SEP events, especially at lower energies.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00180338

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5

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The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft (1977)

Krimigis, S. M. ; Armstrong, T. P. ; Axford, W. I. ; [et al.]

Springer

Space science reviews 21 (1977), S. 329-354

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ISSN: 1572-9672

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft is designed to provide comprehensive measurements of energetic particles in the Jovian, Saturnian, Uranian and interplanetary environments. These measurements will be used in establishing the morphology of the magnetospheres of Saturn and Uranus, including bow shock, magnetosheath, magnetotail, trapped radiation, and satellite-energetic particle interactions. The experiment consists of two subsystems, the Low Energy Magnetospheric Particle Analyzer (LEMPA) whose design is optimized for magnetospheric measurements, and the Low Energy Particle Telescope (LEPT) whose design is optimized for measurements in the distant magnetosphere and the interplanetary medium. The LEMPA covers the energy range from ∼10 keV to 〉 11 MeV for electrons and from ∼15 keV to ≳ 150 MeV for protons and heavier ions. The dynamic range is ∼0.1 to ≳ 1011 cm−2 sec−1 sr−1 overall, and extends to 1013 cm−2 sec−1 sr−1 in a current mode operation for some of the sensors. The LEPT covers the range ∼0.05 ≤ E ≳ 40 MeV/nucleon with good energy and species resolution, including separation of isotopes over a smaller energy range. Multi-dE/dx measurements extend the energy and species coverage to 300–500 MeV/nucleon but with reduced energy and species resolution. The LEPT employs a set of solid state detectors ranging in thickness from 2 to ∼2450 μ, and an arrangement of eight rectangular solid state detectors in an anticoincidence cup. Both subsystems are mounted on a stepping platform which rotates through eight angular sectors with rates ranging from 1 revolution per 48 min to 1 revolution per 48 sec. A ‘dome’ arrangement mounted on LEMPA allows acquisition of angular distribution data in the third dimension at low energies. The data system contains sixty-two 24-bit sealers accepting data from 88 separate channels with near 100% duty cycle, a redundant 256-channel pulse height analyzer (PHA), a priority system for selecting unique LEPT events for PHA analysis, a command and control system, and a fully redundant interface with the spacecraft. Other unique features of the LECP include logarithmic amplifiers, particle identifiers, fast (∼15 ns FWHM) pulse circuitry for some subsystems, inflight electronic and source calibration and several possible data modes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00211545

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6

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Initial observations of low energy charged particles near the Earth's bow shock on ISEE-1 (1979)

Ipavich, F. M. ; Gloeckler, G. ; Fan, C. Y. ; [et al.]

Springer

Space science reviews 23 (1979), S. 93-101

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ISSN: 1572-9672

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract We report initial measurements from the ULECA sensor of the Max-Planck-Institut/University of Maryland experiment on ISEE-1. ULECA is an electrostatic deflection — total energy sensor consisting of a collimator, deflection analyzer and an array of solid state detectors. The position of a given detector, which determines the energy per charge of an incident particle, together with the measured energy determine the particle's charge state. We find that a rich variety of phenomena are operative in the transthermal energy regime (∼10 keV/Q to ∼100 keV/Q) covered by ULECA. Specifically, we present observations of locally accelerated protons, alpha particles, and heavier ions in the magnetosheath and upstream of the Earth's bow shock. Preliminary analysis indicates that the behavior of these locally accelerated particles is most similar at the same energy per charge.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00174113

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