7 research outputs found
Temperature dependence of germylene reactions with acetylene, trimethylsilane, and phenylgermane
No full textCopyright © 2000 Elsevier Science B.V. All rights reserved.Gas-phase reaction rate constants have been determined over the temperature range 295–436 K for the reactions of germylene, GeH₂, with acetylene (GeH₂ addition across a triple bond), trimethylsilane (GeH₂ insertion into a Si–H bond), and phenylgermane. The room-temperature rate constant for germylene reacting with benzene has been measured and is found to be a factor of 300 smaller than that for phenylgermane, indicating that the latter reacts by GeH₂ insertion into the Ge–H bonds. A negative temperature dependence is observed in all cases. The activation energies, obtained from weighted linear fits to the data over the experimental temperature range, are −3.5±0.3, −11.0±0.4, and −3.6±0.3 kJ mol⁻¹ for acetylene, trimethylsilane, and phenylgermane, respectively, while the respective frequency factors, log(A/cm³ molecule⁻¹ s⁻¹), are −10.5±0.1, −11.8±0.1, −10.1±0.1.http://www.sciencedirect.com/science/journal/0009261
Fig. 6 in On a new species of Sundathelphusa Bott, 1969 (Crustacea: Brachyura: Gecarcinucidae) from southeastern Borneo
No full textFig. 6. Sundathelphusa aspera Ng & Stuebing, 1989. A, B, holotype male (42.6 × 32.8 mm) (ZRC 1989.2143), Sabah; C, male (32.3 × 25.4 mm) (ZRC 2014.845), Temburong, Brunei. A, anterior thoracic sternum and male abdomen; B, C, male abdomen.Published as part of Ng, Peter K. L., 2015, On a new species of Sundathelphusa Bott, 1969 (Crustacea: Brachyura: Gecarcinucidae) from southeastern Borneo, pp. 494-502 in Raffles Bulletin of Zoology 63 on page 499, DOI: 10.5281/zenodo.538598
Differential cross sections and spin density matrix elements for the reaction γp→pω
No full textHigh-statistics differential cross sections and spin-density matrix elements for the reaction γp→pω have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide c.m. energy bins, each subdivided into cosθc.m.ω bins of width 0.1. These are the most precise and extensive ω photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.</p
Partial wave analysis of the reaction γp→pω and the search for nucleon resonances
No full textAn event-based partial wave analysis (PWA) of the reaction γp→pω has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world’s first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of ω→π+π-π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F15(1680) and D13(1700) near threshold, as well as the G17(2190) at higher energies. Suggestive evidence for the presence of a JP=5/2+ state around 2 GeV, a “missing” state, has also been found. Evidence for other states is inconclusive.</p
Differential cross sections for the reactions γp→pη and γp→pη'
No full textHigh-statistics differential cross sections for the reactions γp→pη and γp→pη' have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The η' results are the most precise to date and provide the largest energy and angular coverage. The η measurements extend the energy range of the world’s large-angle results by approximately 300 MeV. These new data, in particular the η' measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.</p
Differential photoproduction cross sections of the Σ0(1385), Λ(1405), and Λ(1520)
No full textWe report the exclusive photoproduction cross sections for the Σ0(1385), Λ(1405), and Λ(1520) in the reactions γ+p→K++Y∗ using the CLAS detector for energies from near the respective production thresholds up to a center-of-mass energy W of 2.85 GeV. The differential cross sections are integrated to give the total exclusive cross sections for each hyperon. Comparisons are made to current theoretical models based on the effective-Lagrangian approach and fit to previous data. The accuracy of these models is seen to vary widely. The cross sections for the Λ(1405) region are strikingly different for the Σ+π−, Σ0π0, and Σ−π+ decay channels, indicating the effect of isospin interference, especially at W values close to the threshold.</p
Measurement of the Σπ photoproduction line shapes near the Λ(1405)
No full textThe reaction γ+p→K++Σ+π was used to determine the invariant mass distributions or “line shapes” of the Σ+π−, Σ−π+, and Σ0π0 final states, from threshold at 1328 MeV/c2 through the mass range of the Λ(1405) and the Λ(1520). The measurements were made with the CLAS system at Jefferson Lab using tagged real photons, for center-of-mass energies 1.95</p
