1,725,016 research outputs found
First observation of the decay ≡<sub>c</sub><sup>+</sup>→≡<sup>0</sup>e<sup>+</sup>ν<sub>e</sub> and an estimate of the ≡<sub>c</sub><sup>+</sup> ≡<sub>c</sub><sup>0</sup> lifetime ratio
No full textUsing the CLEO II detector at the Cornell Electron Storage Ring we have observed the decay modes ≡<sub>c</sub><sup>+</sup>→≡<sup>0</sup>e<sup>+</sup>ν<sub>e</sub> and ≡<sub>c</sub><sup>0</sup>→ ≡<sup>-</sup>e<sup>+</sup>V<sub>e</sub> by the detection of a ≡-positron pair of appropriate invariant mass. We find B(≡<sub>c</sub><sup>+</sup>→≡<sup>0</sup>e<sup>+</sup>ν<sub>e</sub>)σ(e<sup>+</sup>e<sup>-</sup>→≡<sub>c</sub><sup>+</sup>X) = 1.55±0.33±0.25 pb, B(≡<sub>c</sub><sup>0</sup>→≡<sup>-</sup>e<sup>+</sup>ν<sub>e</sub>)σ(e<sup>+</sup>e<sup>-</sup>→≡<sub>c</sub><sup>0</sup>X) = 0.63±0.12±0.10 pb, B(≡<sub>c</sub><sup>+</sup>→≡-π<sup>+</sup>π<sup>+</sup>)/B(≡<sub>c</sub><sup>+</sup>→≡<sup>0</sup>e<sup>+</sup>ν<sub>e</sub>) = 0.44±0.11<sub>-0.06</sub><sup>+0.11</sup>, and B(≡<sub>c</sub><sup>0</sup>→≡<sup>-</sup>π<sup>+</sup>)/B(≡<sub>c</sub><sup>0</sup>→≡-e<sup>+</sup>ν<sub>e</sub>) = 0.32±0.10<sub>-0.03</sub><sup>+0.05</sup>. Assuming the ≡<sub>c</sub><sup>+</sup> and ≡<sub>c</sub><sup>0</sup> are equally produced in e<sup>+</sup>e<sup>-</sup> annihilation events at 10 GeV, the lifetime ratio of ≡<sub>c</sub><sup>+</sup>/≡<sub>c</sub><sup>0</sup> is measured to be 2.46±0.70<sub>-0.23</sub><sup>+0.33</sup>
Coupled electron pair calculations for R–C≡E molecules (E = N, P, As or Sb)
No full textThe effect of substituents R (R = H, H 3 C, F or H 5 C 6) on C≡E groups in alkylidyne compounds R - C ≡ E (E = N, P, As or Sb) has been studied at the level of valence electron CEPA (coupled electron pair approximation) calculations. Although the reactivities of R-C ≡ E compounds differ widely (depending on E), the isolated molecules all have surprisingly similar electronic structures. For the H, H 3,C and F species, our calculated bond lengths r e,(R- C) and r e,(C ≡E) agree well with experimental values where such are known. Along with the force constants, some trends for the changes in bond strength emerge. A plausible dependence of the dipole moments on E is observed. For benzonitrile (H 5 C 6 - C ≡N), published experimental values of the C - C( ≡ N) bond length differ. The problem is explored using several basis sets and methods to obtain a value of 1.436(10)A. The C...C( ≡P) bond length in benxylidynephosphane (H 5,C6,-C≡P) is calculated to be 1.435(10)A. Possible uncertainties of some of the experimental values are discussed
Molecular tapes based on C≡N···Cl interactions
No full textWeak C≡N ··· Cl interactions may be used to design linear molecular tapes
Photoelectron spectra of methylidynephosphanes R-C≡P (Gasphase reactions ; 31)
No full textDie PE-spektroskopische Optimierung thermischer Zersetzungsreaktionen in der Gasphase wird auf die Chlor[(trimethylsilyl)methylen]phosphan-Derivate ((H3C)3Si)RC = PCl mit R = C6H5, Si(CH3)3 angewendet. In einer Kurzweg-Pyrolyse spaltet sich bei 1300 K quantitativ (H3C)3SiCl ab. Die gebildeten Methylidinphosphane (H3C)3Si-C-P und C6H5-C≡P lassen sich durch einen Vergleich ihrer PE-Spektren mit dem des stabilen tert-Butyl-Derivates (H3C)3-C≡P nachweisen und charakterisieren.The PE spectroscopic optimization of thermal decomposition reactions in the gaseous phase has been applied to the chloro[(trimethylsily)methylene]phosphane derivaties ((H3C)3Si)RC = PCI with R = C6H5. Si(CH3)3. In a short-path pyrolysis, (H3C)3SiCl is split off quantitatively at 1300 K. The methylidynephosphanes formed, (H3C)3Si C- P and C6H5- C≡ P, can be detected and characterized by comparison of their PE spectra with that of the stable tert-butyl derivative, (H3C)3-C≡ P
[P≡C-S]−[Li(dme)3]+ : synthesis and structure (Alkylidynephosphanes and -arsanes ; 1)
No full textO,O′-Diethylthiocarbonat setzt sich mit Bis-(tetrahydrofuran)lithium-bis(trimethylsilyl)phosphanid in 1,2-Dimethoxyethan unterhalb 0°C zu Ethoxy-trimethylsilan und Tris(1,2-dimethoxyethan-O,O′)lithium-2λ3-phosphaethinylsulfanid – [P≡C-S]−[Li(dme)3] – (1a) um. Das als dunkelrote, konzentrierte Lösung erhaltene λ3-Phosphaalkin 1 entsteht neben Bis(trimethylsilyl)sulfan bzw. Kohlenstoffoxidsulfid auch bei den Umsetzungen von Kohlenstoffdisulfid mit Bis(tetrahydrofuran)lithium-bis(trimethylsilyl)phosphanid oder dem homologen Lithoxy-methylidinphosphan P≡C-O-Li (2) [1]. Das IR-Spektrum weist die für eine P≡C- und C-S-Valenzschwingung charakteristischen Absorptionen bei 1762 und 747 cm-1 auf; die NMR-Parameter {δ(31P) -121,3; δ(13C) 190,8 ppm; 1JCP 18,2 Hz} gleichen mehr den Werten der Diorganylamino-2λ3-phosphaalkine als des Bis(1,2-dimethoxyethan-O,O′)-lithoxy-methylidinphosphans (2a). Nach den Ergebnissen einer Röntgenstrukturanalyse (P21/c; a = 1192,6(16); b = 1239,1(19); c = 1414,8(26) pm; β = 105,91(13)° bei -100 ± 3°C; Z = 4 Formeleinheiten; wR = 0,064) an blaßgelben, aus einem Ansatz mit O,O′-Diethylthiocarbonat isolierten Kristallen (Schmp. +16°C) liegen im Festkörper getrennte [P≡C-S]−- und [Li(dme)3]+-Ionen vor. Charakteristische Bindungslängen und -winkel sind: P≡C 155,5(11); C-S 162,0(11); Li-O 206,4(17) bis 220,3(20) pm; P≡C-S 178,9(7)°.O,O′-Diethyl thiocarbonate and bis(tetrahydrofuran)-lithium bis(trimethylsilyl)phosphanide dissolved in 1,2-dimethoxyethane, react below 0°C to give ethoxy trimethylsilane and tris(1,2-dimethoxyethane-O,O′)lithium 2λ3-phosphaethynylsulfanide – [P≡C-S]− [Li(dme)3] – (1a). Apart from bis(trimethylsilyl)sulfane or carbon oxide sulfide, dark red concentrated solutions of λ3-phosphaalkyne 1 are also obtained from reactions of carbon disulfide with bis(tetrahydrofuran)-lithium bis(trimethylsilyl)phosphanide or with the homologous lithoxy-methylidynephosphane (2) [1]. The ir spectrum shows two absorptions at 1762 and 747 cm-1 characteristic for the P≡C and C-S stretching vibrations. The nmr parameters {δ(31P) -121.3; δ(13C) 190.8 ppm; 1JCP 18.2 Hz} resemble much more values of diorganylamino-2λ3-phosphaalkynes than those of bis(1,2-dimethoxyethane-O,O′)lithoxy-methylidyne-phosphane (2a). As found by an X-ray structure analysis (P21/c; a = 1192.6(16); b = 1239.1(19); c = 1414.8(26) pm; β = 105.91(13)° at -100 ± 3°C; Z = 4 formula units; wR = 0.064) of pale yellow crystals (mp. +16°C) isolated from the reaction with O,O′-diethyl thiocarbonate, the solid is built up of separate [P≡C-S]− and [Li(dme)3]+ ions. Typical bond lengths and angles are: P≡C 155.5(11); C-S 162.0(11); Li-O 206.4(17) to 220.3(20) pm; P≡C-S 178.9(7)°
Relativistic ≡ method for<SUP> </SUP>atoms
No full textApproximate relativistic corrections to the atomic radial wave functions of the recently reported ≡ method are presented based on the approach of Cowan and Griffin. The major relativistic effects are shown to be incorporated into the wave function while retaining the nonrelativistic format. The one-electron eigenvalues, total energies, expectation values of rn for n=-1,1, and 2 and spin-orbit parameter values are reported. The results are comparable with the fully relativistic Dirac-Hartree-Fock values
California Poll: 8801 -- February 17-21, 1988
No full textThe Field Poll, established in 1945 as The California Poll by Mervin Field, has operated continuously as an independent, non-partisan, media-sponsored public opinion news service. Each year the Field Polls cover a wide range of political and social topics examining California public opinion. Continuing measures are made of voter support for leading political figures vying for major state and federal offices, job ratings of important political figures and reactions to significant political events. Voter awareness, understanding and predispositions of major campaign issues and salient statewide ballot propositions are also tracked over time. For poll 8801 N=1011
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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