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Chemistry

Portland State University

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Articles 271 - 277 of 277

Full-Text Articles in Physical Sciences and Mathematics

Existence Of High-Order Superlattices In Orientationally Ordered C_{60}, J. E. Fischer, D. E. Luzzi, K. Kniaź, A. R. Mcghie, D. A. Ricketts-Foot, W. R. Romanow, Gavin B. M. Vaughan, Dayin Li, Allan L. Smith, Robert M. Strongin, M. A. Cichy, Laurent Bard, Amos B. Smith Iii Jun 1993

Existence Of High-Order Superlattices In Orientationally Ordered C_{60}, J. E. Fischer, D. E. Luzzi, K. Kniaź, A. R. Mcghie, D. A. Ricketts-Foot, W. R. Romanow, Gavin B. M. Vaughan, Dayin Li, Allan L. Smith, Robert M. Strongin, M. A. Cichy, Laurent Bard, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

We correlate the presence or absence of high-order modulated structures in solid C60 with the differential scanning calorimetry signature of the orientational ordering transition and other diagnostic data. We have searched for, but not observed, the 2a face-centered cubic structure recently observed in low-temperature electron and single-crystal x-ray diffraction. We conclude that the intrinsic ground state is the previously reported simple cubic structure [space groupPa3¯, a(14 K)=14.06 Å], and that other structures may be stabilized by defects or impurities.

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Coherence Peak And Superconducting Energy Gap In Rb_{3}C_{60} Observed By Muon Spin Relaxation, R. F. Kiefl, W. A. Macfarlane, K. H. Chow, S. Dunsiger, T. L. Duty, T. M. S. Johnston, J. W. Schneider, J. Sonier, Laurent Brard, Robert M. Strongin, J. E. Fischer, Amos B. Smith Iii Jun 1993

Coherence Peak And Superconducting Energy Gap In Rb_{3}C_{60} Observed By Muon Spin Relaxation, R. F. Kiefl, W. A. Macfarlane, K. H. Chow, S. Dunsiger, T. L. Duty, T. M. S. Johnston, J. W. Schneider, J. Sonier, Laurent Brard, Robert M. Strongin, J. E. Fischer, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

Muon spin relaxation resulting from spin exchange scattering of endohedral muonium (μ+e-) with thermal electronic excitations has been observed in the fullerene superconductor Rb3C60. The temperature dependence of T1-1 shows a coherence peak just below Tc and can be fit to the conventional Hebel-Slichter theory for spin relaxation in a superconductor with a broadened BCS density of states. The average energy gap for electronic excitations, Δ/kB=53(4) K or 2Δ/ kBTc=3.6(3), is consistent with the BCS weak coupling limit.

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Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii May 1993

Unusual Thermal Stability Of A Site-Ordered Mc60 Rocksalt Structure (M=K, Rb, Or Cs), Q. Zhu, O. Zhou, J. E. Fischer, Andrew R. Mcghie, W. R. Romanow, Robert M. Strongin, M. A. Cichy, Amos B. Smith Iii

Chemistry Faculty Publications and Presentations

X-ray diffraction and differential scanning calorimetry of MxC60, with x∼1 and M=K, Rb, or Cs, reveal an unusual T-dependent phase sequence. A low-symmetry ground state is found, while the high-T limit is an ordered rocksalt structure in which only the octahedral sites are occupied. The unusual high-T stability of this ordered phase is attributed to the entropy of molecular orientational disorder and/or thermal disorder of the alkali-metal ions within the octahedral sites. Unique to KxC60 with x≥1.4, we find at intermediate temperatures an fcc site-disordered lattice gas …

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Bis(1h+-Pyrazinium N4-Oxide) Dichromate, Gary L. Gard, Roger D. Willett, W. W. Paudler, R. M. Sheets, Mark R. Pressprich Sep 1990

Bis(1h+-Pyrazinium N4-Oxide) Dichromate, Gary L. Gard, Roger D. Willett, W. W. Paudler, R. M. Sheets, Mark R. Pressprich

Chemistry Faculty Publications and Presentations

2C₄H₅N₂O⁺.Cr₂O²₇⁻, Mᵣ=410∙2, monoclinic, P2₁, a=8∙(2), b=6∙132 (2), c=14∙493 (4) Å, β=94∙50 (2)°, V=708∙8 (3) ų, Z=2, Dₓ=1∙92 g cm⁻³, Mο Κα, λ=0∙71069 Å, μ=15∙5 cm⁻¹, F(000)=412, T=293 K, R=0∙0602 for 1980 unique observed reflections with F≥3σ(F). The structure consists of discrete dinegative dichromate anions hydrogen bonded to monopositive pyrazinium N-oxide cations (N―H∙∙∙O=2∙724, 2∙644 Å). A strong hydrogen bond to the bridging O atom in the Cr₂O²₇⁻ anion leads to significant lengthening of the bridging Cr―O bonds. A short C―H∙∙∙O interaction (3∙180 Å) is also observed.

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Medium Resolution Atmospheric Pressure Ionization Mass Spectrometer, Andrew H. Grange, Robert J. O'Brien, Douglas F. Barofsky Jan 1988

Medium Resolution Atmospheric Pressure Ionization Mass Spectrometer, Andrew H. Grange, Robert J. O'Brien, Douglas F. Barofsky

Chemistry Faculty Publications and Presentations

An atmospheric pressure ionization (API) source for a VG 7070E‐HF mass spectrometer has been built and successfully operated at an accelerating potential of 6 kV. Hydrated protons and hydrated organic ions formed in the API source can be either partially or completely disaggregated by collisionally induced dissociation before entering the mass analyzer. The protonated molecular ions of pinacolone and 2,4‐pentanedione can be fully separated (R=2800, m/z 101,

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Generalized Response Of Chemiluminescence Analyzers, A. A. Mehrabzadeh, Robert J. O'Brien, Thomas M. Hard Aug 1983

Generalized Response Of Chemiluminescence Analyzers, A. A. Mehrabzadeh, Robert J. O'Brien, Thomas M. Hard

Chemistry Faculty Publications and Presentations

The mass flow and chemical kinetic equations for a gaseous chemiluminescence (CL) analyzer are formulated and solved. The resultant equation can be used to predict the absolute response of the analyzer as a function of the sample flow rate, the sample gas pressure, the chamber pressure, the chamber volume, the mass flow rate and mole fraction of the reagent gas, and the rate constants of the relevant chemical processes. Thus, the equation allows optimization of these parameters. It is shown that for varying sample pressure the analyzer can be used to measure either concentration or mole fraction and that interfering …

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Pressure Dependence Of Fluorescent And Photolytic Interferences In Ho Detection By Laser-Excited Fluorescence, Thomas M. Hard, Robert J. O'Brien, T. B. Cook Jul 1980

Pressure Dependence Of Fluorescent And Photolytic Interferences In Ho Detection By Laser-Excited Fluorescence, Thomas M. Hard, Robert J. O'Brien, T. B. Cook

Chemistry Faculty Publications and Presentations

In the measurement of HO concentrations by laser-excited fluorescence, expansion of the sampled air offers a way to reduce fluorescent and photolytic interference by other species. The decrease in [HO] upon expansion is balanced by an increase in HO fluorescence yield over a wide range of pressures. Background air fluorescence is reduced if the responsible species have fluorescence yields higher than those of HO. Preliminary experiments indicate that most of the fluorescence observed in laboratory air is due to such species. Upon expansion, the suppression of fluorescent interference can be no greater than the reduction in pressure, whereas the suppression …

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