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  • 1
    Digitale Medien
    Digitale Medien
    Variation of γ-Ray and Particle Fluxes At the Sea Level During the Total Solar Eclipse of 24 October, 1995 (1997)
    Springer
    Astrophysics and space science 250 (1997), S. 313-326 
    Details
    ISSN: 1572-946X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A Total Solar Eclipse (TSE) was observed from Diamond Harbour (lat. 22.2°N, long 88.2°E) on 24 October 1995. The variation of γ-ray intensity was measured in the energy range of 0.3–3.0 MeV for different time spans throughout the period of the eclipse. A CR-39 detector was used to look at the change in the fluxes of neutral and charged particles. The maximum drop (∼ 25%) in the intensity of γ-ray was observed in the range 2.5–3 MeV during TSE. The CR-39 results showed the appearance of a good number of tracks and a small variation of proton and neutron flux of ≤ 10% which was not significant statistically. Low energy γ-ray fluxes at sea level originate from the secondary electron-photon components of cosmic rays in the atmosphere; its modulation by TSE is interpreted as follows. The cooling of the atmosphere in the path of the umbra induces a reduction of the height of the main production layer of the nuclear component, as a result of which, fewer µ± mesons (from the decay of theπ± mesons) decay to e±. This leads to a small reduction in the flux of electron-photon component at sea level which originates from this branch; the main branch of e - γ component from π0 decay remains nearly unaffected. As the total mass of air remains the same, little or no change in the slow proton or the neutron flux at sea level is expected. These are consistent with the present observations. For a better understanding, further studies of this new phenomenon during future TSE are suggested.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1000408422978
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  • 2
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of thiocyanate anation ofcis-β-diaqua-(3,6-diazaoctane-1,8-diamine)cobalt(III) in aqueous medium (1985)
    Springer
    Transition metal chemistry 10 (1985), S. 252-254 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Kinetic studies of the anation of the title complex by NCS− show that it occurs in a stepwise manner leading to thecis-β-dithiocyanato complex, both steps having a common rate equation (1): (1) $$k_{obs} = k' + \frac{{k \cdot Q[NCS^ - ]}}{{1 + {\text{Q[NCS]}}}}.$$ The variation ofpseudo-first-order rate constant with pH shows that for the first step k increases with increase in pH (in the 1.8–2.8 range) whereas it remains fairly constant for the second step. Acis-labilisation effect of the hydroxo-group arising from the protic equilibrium of the parent complex is operative and the reaction proceeds through a dissociative interchange process. The activation parameters corresponding to the k' and k paths for each of the steps have been evaluated and compare well with those reported for similar systems.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00621080
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  • 3
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the reduction of dodecatungstocobaltate(III) by α-hydroxyacids in aqueous acid solution. Evidence for alkali metal ion catalysis (1991)
    Springer
    Transition metal chemistry 16 (1991), S. 160-164 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The kinetics of the redox reaction of dodecatungstocobaltate(III) [abbreviated as CoIIIW] with three α-hydroxy-carboxylic acids:e.g., mandelic, glycolic and lactic acid, were investigated in the 0–5.4 pH range where the complex remains stable and does not decompose. All reactions are first-order both in oxidant and reductant over the experimental pH range. A specific metal ion effect has been observed. Oxidations of the molecular form of the three acids and the anionic form of mandelic acid are catalysed by alkali metal ions and follow a general rate law: $$ - d[Co^{III} W]/dt = 2(k_s + k_c [M^ + ])[R][Co^{III} W]$$ where ks and kc account for the spontaneous and catalysed paths respectively, M+ is either an alkali metal ion (Li+, Na+ or K+) and [R], the reductant concentration. The oxidation of lactate and glycolate ions occurs only in the presence of alkali cations. The cation catalytic order: K+〉Na+〉Li+ observed in this study is in accord with the polarizability of the cations. An outer-sphere alkali cation-bridged mechanism is suggested for the electron transfer step.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01032824
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  • 4
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the reaction oftrans-cyclohexane-1,2-diamine-N N N' N'-tetra-acetatomanganate(III) with substituted thioureas in aqueous medium (1991)
    Springer
    Transition metal chemistry 16 (1991), S. 355-357 
    Details
    ISSN: 1572-901X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The kinetics of reduction of [MnIII(cydta)]− (where H4cydta=trans-cyclohexane-1,2-diamine-N N N' N'-tetraacetic acid) by some thiourea reductants have been studied in aqueous solution by stopped-flow techniques in the pH ranges 2.5–4.5 and 9.2–10.2. An initial increase in absorbance followed by a steady decrease indicated the formation of a precursor complex prior to the electron transfer step. The reactions are first order in both oxidant and reductant. The observed increase in rate in going from low to high pH is attributed to the difference in reactivities of the aqua and hydroxo species of the MnIII complex; the higher reactivity of the latter is consistent with the formation of a ligand-bridged activated species prior to electron transfer. The reactivity order for the thiourea derivatives follows the order of their reported substituent effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01024082
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  • 5
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the alkali metal ions promoted electron transfer between 12-tungstocobaltate(III) and citric acid (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 20 (1988), S. 699-712 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the interactions of the Keggin type heteropolyanion [CoW12O40]5-, with all the molecular and anionic forms of citric acid have been investigated spectrophotometrically in the pH range 0.60-5.45 at 60°C. With the exception of the molecular form of the acid (H3L), all the other species (H2L-, HL2-, and L3-) undergo oxidation through an alkali metal ion catalyzed path in addition to the uncatalyzed one. The catalytic power increases with increasing size of the alkali metal ion. The contributions of each path have been evaluated from the kinetic data with the help of the measured dissociation constant values of citric acid. A plausible mechanism involving the formation of a bridged outer-sphere complex of the reacting species with the alkali cation, has been suggested. The observed limiting dependence of kobs on [citrate] at high concentrations owing to an equilibrium between the reactants preceeding the electron transfer step supports the proposed mechanism. The pH-rate profile gives an excellent fit with the evaluated kinetic parameters.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/kin.550200904
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  • 6
    Digitale Medien
    Digitale Medien
    Kinetics and mechanism of the oxidation of some cyclic and acyclic ketones by dodecatungstocobaltate(III) - A comparative study (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 22 (1990), S. 81-94 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of oxidation of cyclohexanone(chxn), 2-butanone(but), and 1,3-dihydroxy-2-propanone (dhp) have been investigated in aqueous acidic media. A first-order dependence in complex is obtained at high acid and low oxidant concentration for these ketones. However, a zero-order rate prevails at high oxidant and low acid concentration, and this rate has been shown to be the acid catalyzed enolization rate of the ketone. A general rate expression has been derived to explain these behaviors and plausible mechanism has been offered by assuming the enol as the reactive species.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/kin.550220107
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  • 7
    Digitale Medien
    Digitale Medien
    Kinetics of electron transfer reactions of manganese (III) complexes of trans-cyclohexane-1,2-diamine,-NNN′N′-tetraacetic acid and 2,2′-bipyridyl with ascorbic acid in aqueous acid media (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 23 (1991), S. 105-112 
    Details
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the reactions of manganese(III) complexes of trans-cyclohexane-1,2-diamine-NNN′N′-tetraacetic acid (H4cydta) and 2,2′-bipyridyl (bpy) have been investigated in the acid ranges [H+] = 1.00 ×10-5 - 3.16 × 10-3 M and [H+] = 0.10 - 1.00 M, respectively, at different temperatures and at a constant ionic strength. Both the molecular and mono-anionic forms of ascorbic acid have been found to be reactive in the experimental acid ranges. The monoanionic species has been found to be more reactive than the molecular form. Attempts have been made to correlate the kinetic results in terms of the Marcus relationship for outer-sphere electron transfer reaction. Differences between the calculated rates (k0.8) and experimental rates (k) by approximately four and seven orders of magnitude (k0.8≪ k) suggest an innersphere pathway for the reaction of Mn(cydta)(H2O)-. Inner-sphere reaction is also believed to be operative for the other reaction. The activation parameters have been evaluated and compared with other reported systems.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/kin.550230202
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