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41.
The rate of decomposition of isopropyl nitrite (IPN) has been studied in a static system over the temperature range of 130–160°C. For low concentrations of IPN (1–5 × 10?5M), but with a high total pressure of CF4 (~0.9 atm) and small extents of reaction (~1%), the first-order rates of acetaldehyde (AcH) formation are a direct measure of reaction (1), since k3 » k2(NO): \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$ {\rm IPN}\begin{array}{rcl} 1 \\ {\rightleftarrows} \\ 2 \\ \end{array}i - \Pr \mathop {\rm O}\limits^. + {\rm NO},i - \Pr \mathop {\rm O}\limits^. \stackrel{3}{\longrightarrow} {\rm AcH} + {\rm Me}. $\end{document} Addition of large amounts of NO (~0.9 atm) in place of CF4 almost completely suppressed AcH formation. Addition of large amounts of isobutane – t-BuH – (~0.9 atm) in place of CF4 at 160°C resulted in decreasing the AcH by 25%. Thus 25% of \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^{\rm .} $\end{document} were trapped by the t-BuH (4): \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + t - {\rm BuH} \stackrel{4}{\longrightarrow} i - \Pr {\rm OH} + (t - {\rm Bu}). $\end{document} The result of adding either NO or t-BuH shows that reaction (1) is the only route for the production of AcH. The rate constant for reaction (1) is given by k1 = 1016.2±0.4–41.0±0.8/θ sec?1. Since (E1 + RT) and ΔH°1 are identical, within experimental error, both may be equated with D(i-PrO-NO) = 41.6 ± 0.8 kcal/mol and E2 = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result that \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta H_f^\circ (i - {\rm Pr}\mathop {\rm O}\limits^{\rm .} ) = - 11.9 \pm 0.8{\rm kcal}/{\rm mol}. $\end{document} From ΔS°1 and A1, k2 is calculated to be 1010.5±0.4M?1·sec?1. From an independent observation that k6/k2 = 0.19 ± 0.03 independent of temperature we find E6 = 0 ± 1 kcal/mol and k6 = 109.8+0.4M?;1·sec?1: \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + {\rm NO} \stackrel{6}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} In addition to AcH, acetone (M2K) and isopropyl alcohol (IPA) are produced in approximately equal amounts. The rate of M2K formation is markedly affected by the ratio S/V of different reaction vessels. It is concluded that the M2K arises as the result of a heterogeneous elimination of HNO from IPN. In a spherical reaction vessel the first-order rate of M2K formation is given by k5 = 109.4–27.0/θ sec?1: \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm IPN} \stackrel{5}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} IPA is thought to arise via the hydrolysis of IPN, the water being formed from HNO. This elimination process explains previous erroneous results for IPN. 相似文献
42.
Veerasamy V.S. Amaratunga G.A.J. Milne W.I. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(3):322-328
A model is proposed for the flow of a plasma originating from a cathodic vacuum arc into a curvilinear magnetic field. The model gives good agreement with measurements obtained from a filtered cathodic-arc thin film deposition system. The important parameters involved in the motion of a vacuum arc plasma beam through a magnetic filter are examined. The analysis is based on the use of the guiding center approximation to describe the motion of the charged particles produced in the plasma where the thermal energy is negligible compared to the mass flow energy. Electron-ion collision effects are included within the framework of the drift model. It is shown that under the limiting condition of a collision frequency which is much higher than the cyclotron frequency of the electron, the motion of the plasma ions around the bend becomes independent of the magnetic field, with the number of ions traversing the filter significantly reduced. However, in the collisionless plasma case (cyclotron frequency higher than the collision frequency), the model predicts a square-law relationship between ion-saturation current and magnetic field , I p ∞B 2 相似文献
43.
Bilek M.M.M. McKenzie D.R. Yongbai Yin Chhowalla M.U. Milne W.I. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(5):1291-1298
Curved magnetic ducts are frequently used to remove macroscopic-sized droplets from the plasma stream of cathodic vacuum arcs. The plasma of a cathodic vacuum arc in a magnetic filter is characterized by a strongly directional ion velocity (corresponding to 20-100 eV) and magnetized electrons. In the first section of this paper the effects of these features on the I-V characteristic curves of planar probes are identified and explained using a simple model. This is then used to interpret the interaction of the plasma with the walls of a biased quarter torus duct. Two small electrodes placed on the outer and inner sections of the curved duct wall show that the I-V characteristic is determined primarily by the electron-ion current balance at the wall on the outside of the curve. The application of a bias to a planar electrode on the outer wall section was found to give the same increase in throughput as a positive bias applied to the entire duct with the advantage of a much smaller electron current being drawn by the biasing power supply. The improvement in duct throughput achievable with positive-biasing of the duct wall was found to depend on both the configuration and strength of the magnetic field in the quarter torus filter. The plasma density profile and potential were unaffected by the application of the bias 相似文献
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The rate of decomposition of t-butyl nitrite (TBN) has been studied in a static system over the temperature range of 120–160°C. For low concentrations of TBN (10?5- 10?4M), but with a high total pressure of CF4 (~0.9 atm) and small extents of reaction (~1%), the first-order homogeneous rates of acetone (M2K) formation are a direct measure of reaction (1), since k3» k2 (NO): TBN . Addition of large amounts of NO in place of CF4 almost completely suppresses M2K formation. This shows that reaction (1) is the only route for this product. The rate of reaction (1) is given by k1 = 1016.3–40.3/θ s?1. Since (E1 + RT) and ΔH are identical, both may be equated with D(RO-NO) = 40.9 ± 0.8 kcal/mole and E2 = O ± 1 kcal/mole. From ΔS and A1, k2 is calculated to be 1010.4M?1 ·s?1, implying that combination of t? BuO and NO occurs once every ten collisions. From an independent observation that k2/k2′ = 1.7 ± 0.25 independent of temperature, it is concluded that k2′ = 1010.2M?1 · s?1 and k1′ = 1015.9?40.2/θ s?1; . This study shows that MeNO arises solely as a result of the combination of Me and NO. Since NO is such an excellent radical trap for t-Bu\documentclass{article}\pagestyle{empty}\begin{document}${\rm Me\dot O}$\end{document}, reaction (2) may be used in a competitive study of the decomposition of t? Bu\documentclass{article}\pagestyle{empty}\begin{document}${\rm Me\dot O}$\end{document} in order to obtain the first absolute value for k3. Preliminary results show that k3 (∞) = 1015.7–17.0/θ s?1. The pressure dependence of k3 is demonstrated over the range of 10?2?1 atm (160°C). The thermochemistry for reaction (3) implies that the Hg 6(3P1) sensitised decomposition of t-BuOH occurs via reaction (m): In addition to the products accounted for by the TBN radical split, isobutene is formed as a result of the 6-centre elimination of HONO: TBN \documentclass{article}\pagestyle{empty}\begin{document}$\mathop \to \limits^7 $\end{document} isobutene + HONO. The rate of formation of isobutene is given by k7 = 1012.9–33.6/θ s?1. t-BuOH, formed at a rate comparable to that of isobutene–at least in the initial stages–is thought to arise as a result of secondary reactions between TBN and HONO. The apparent discrepancy between this and previous studies is reconciled in terms of the above parallel reactions (1) and (7), such that k + 2k7 = 1014.7–36.2/θ s?1. 相似文献
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A novel phenanthridine, nantradol ( 1 ), resulted from a search to dissect out analgetic activity from the cannabinoid molecule. Nantradol possesses two to seven times greater potency than morphine across a battery of analgetic tests. Despite this morphine-like profile, nantradol does not bind to the opiate receptor. Nantradol has a total of five asymmetric centers and was studied as a 50:50 mixture of two diastereomers, both of which possess the trans 6a, 10a stereochemistry and have β-oriented substituents at positions 6 and 9. Evidence is provided that, in common with the opiates, the analgetic actions of nantradol are stereospecific, the majority of the activity residing in a single levorotatory isomer. The stereospecificity and potency of the analetic effects of the nantradol series suggests a highly specific interaction at an as yet unidentified receptor. 相似文献
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