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21.
Absolute rate constants, k2, for the reaction of OH radicals with 2-methyl-2-butene have been determined over the temperature range 297–425 K using a flash photolysis-resonance fluorescence technique. The Arrhenius expression obtained was k2 = 3.6 × 10?11 exp [(450 ± 400)/RT] cm3 molecule?1 s?1. 相似文献
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23.
The kinetics of the gas phase reactions of NO2 with a series of organics have been studied at 295 ± 2 K. It was observed that only 2,3-dimethyl-2-butene and the conjugated dialkenes studied reacted at observable rates, with rate constants which ranged from 1.5 × 10?20 cm3 molecule?1 s?1 for 2,3-dimethyl-2-butene to 1.3 × 10?17 cm3 molecule?1 s?1 for α-phellandrene. These rate constants are compared with the available literature data and the mechanisms of these reactions are discussed. 相似文献
24.
A rapid and accurate method for the determination of bismuth in rock samples is described. Automated equipment is used to generate bismuth hydride from solutions of rock samples prepared by digestion with a mixture of hydrofluoric and perchloric acids. The evolved hydride is carried to a heated quartz tube by a stream of argon, and the atomic absorption of bismuth recorded. Thiosemicarbazide and 1,10-phenanthroline are used as masking agents to minimize interferences from copper and nickel. As little as 20 ng Bi g-1 can be determined; the average r.s.d. is 5.4%. Results obtained for six USGS standard rocks are in close agreement with the recommended values obtained by an isotope dilution technique. 相似文献
25.
The homogeneous gas-phase reaction of N2H4 with O3 in air atmospheric pressure has been used to generate OH radicals in the dark, allowing the determination of relative OH radical rate constants for compounds which photolyze rapidly. This technique was first validated by determining the OH radical rate constant ratios for n-butane/cyclohexane and methanol/dimethyl ether, both of which are in excellent agreement with the literature values. The rate constant for the reaction of OH radicals with methyl nitrite at 300 ± 3 K was then determined relative to those for the reaction of OH radicals with n-hexane and dimethyl ether. The resulting rate constant of 1.8 × 10?13 cm3/molecule·s is about seven times lower than those of previous measurements which employed a different nonphotolytic relative rate method. 相似文献
26.
James N. Pitts Eugenio Sanhueza Roger Atkinson William P. L. Carter Arthur M. Winer Geoffrey W. Harris Christopher N. Plum 《国际化学动力学杂志》1984,16(7):919-939
The formation of nitrous acid (HONO) in the dark from initial concentrations of NO2 of 0.1–20 ppm in air, and the concurrent disappearance of NO2, were monitored quantitatively by UV differential optical absorption spectroscopy in two different environmental chambers of ca.4300- and 5800-L volume (both with surface/volume ratios of 3.4 m?1). In these environmental chambers the initial HONO formation rate was first order in the NO2 concentration and increased with the water vapor concentration. However, the HONO formation rate was independent of the NO concentration and relatively insensitive to temperature. The initial pseudo-first-order consumption rate of NO2 was (2.8 ± 1.2) × 10?4 min?1 in the 5800-L Teflon-coated evacuable chamber and (1.6 ± 0.5) × 10?4 min?1 in a 4300-L all-Teflon reaction chamber at ca.300 K and ca.50% RH. The initial HONO yields were ca.40–50% of the NO2 reacted in the evacuable chamber and ca.10–30% in the all-Teflon chamber. Nitric oxide formation was observed during the later stages of the reaction in the evacuable chamber, but ca.50% of the nitrogen could not be accounted for, and gas phase HNO3 was not detected. The implications of these data concerning radical sources in environmental chamber irradiations of NOx? organic-air mixtures, and of HONO formation in polluted atmospheres, are discussed. 相似文献
27.
Quantum yields for the production of I(52P) atoms from the photolysis of ICN in the à state continuum are presented as a function of wavelength. Evidence is presented for the existence of at least three electronic states giving rise to the absorption spectra. Primary photophysical processes involved in the dissociation of ICN are discussed. 相似文献
28.
Given an M/G/ queue with input rate and service-time distribution G, we consider the problem of estimating and G from data on the queue-length process Q = (Qt). Our motivation is to study departures of G from exponentiality, following recent work of Bingham and Dunham (1997, Ann. Inst. Statist. Math., 49, 667–679). 相似文献
29.
J. Brian Pitts 《Foundations of Physics》2018,48(5):579-590
Change and local spatial variation are missing in Hamiltonian general relativity according to the most common definition of observables as having 0 Poisson bracket with all first-class constraints. But other definitions of observables have been proposed. In pursuit of Hamiltonian–Lagrangian equivalence, Pons, Salisbury and Sundermeyer use the Anderson–Bergmann–Castellani gauge generator G, a tuned sum of first-class constraints. Kucha? waived the 0 Poisson bracket condition for the Hamiltonian constraint to achieve changing observables. A systematic combination of the two reforms might use the gauge generator but permit non-zero Lie derivative Poisson brackets for the external gauge symmetry of General Relativity. Fortunately one can test definitions of observables by calculation using two formulations of a theory, one without gauge freedom and one with gauge freedom. The formulations, being empirically equivalent, must have equivalent observables. For de Broglie-Proca non-gauge massive electromagnetism, all constraints are second-class, so everything is observable. Demanding equivalent observables from gauge Stueckelberg–Utiyama electromagnetism, one finds that the usual definition fails while the Pons–Salisbury–Sundermeyer definition with G succeeds. This definition does not readily yield change in GR, however. Should GR’s external gauge freedom of general relativity share with internal gauge symmetries the 0 Poisson bracket (invariance), or is covariance (a transformation rule) sufficient? A graviton mass breaks the gauge symmetry (general covariance), but it can be restored by parametrization with clock fields. By requiring equivalent observables, one can test whether observables should have 0 or the Lie derivative as the Poisson bracket with the gauge generator G. The latter definition is vindicated by calculation. While this conclusion has been reported previously, here the calculation is given in some detail. 相似文献
30.