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  • 1
    Electronic Resource
    Electronic Resource
    Mechanism and rate constant of the reaction of atomic hydrogen with propyne (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8458-8465 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surface for the reaction of atomic hydrogen with propyne has been studied at the G3//UB3LYP/6-31G(d) level of theory. Three reaction entrances were revealed, namely, terminal addition, nonterminal addition, and direct H-abstraction, leading to CH3CCH2, CH3CHCH, and H2+C3H3, respectively. The respective activation barriers are 1.7, 3.9, and 8.4 kcal/mol. The CH3-extrusion from CH3CHCH forms C2H2 via a barrier of about 32 kcal/mol. Several H-shift paths along the CCC skeleton were also examined for three C3H5 isomers. Multichannel RRKM and TST calculations have been carried out for the total and individual rate constants over a wide range of temperatures and pressures. The total rate constants possess both positive temperature dependence and typical "S" shaped fall-off behavior. At atmospheric pressure, the collisional stabilization of the initial adducts dominates the H+CH3CCH reaction at temperatures lower than 500 K, and at T〉1000 K, CH3 and C2H2 are the major products. Moreover, the direct H-abstraction channel also contributes significantly to the overall reaction. The theoretical results are compared with those of previous studies. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481484
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  • 2
    Electronic Resource
    Electronic Resource
    The gaseous reaction of vinyl radical with oxygen (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1742-1746 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gaseous reaction of vinyl radical with oxygen has been experimentally investigated. C2H3 radical was produced by laser photolysis of C2H3Br at 248 nm. The vibrationally excited products of the reaction were detected by time-resolved Fourier transform infrared emission spectroscopy. H2CO(ν1), HCO(ν1,ν3), and CO2(ν3) are ascertained as the main emitters. The most favorable product channel is HCO and H2CO. The reaction channel leading to CO2+CH3 has been found for the first time. The minor reactions leading to C2H2+HO2, C2H3O+O, and C2H2O2+H may also occur. A secondary reaction product of CO is observed, which is generated from the primary reaction product HCO. Combining theoretical analysis with the present experimental results, the reaction pathways are clarified. The results are of importance for understanding the combustion processes of hydrocarbon. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1382814
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  • 3
    Electronic Resource
    Electronic Resource
    PSII photochemistry, thermal energy dissipation, and the xanthophyll cycle in Kalanchoë daigremontiana exposed to a combination of water stress and high light (2003)
    Oxford, UK : Munksgaard International Publishers
    Physiologia plantarum 118 (2003), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Kalanchoë daigremontiana, a CAM plant grown in a greenhouse, was subjected to severe water stress. The changes in photosystem II (PSII) photochemistry were investigated in water-stressed leaves. To separate water stress effects from photoinhibition, water stress was imposed at low irradiance (daily peak PFD 150 μmol m−2 s−1). There were no significant changes in the maximal efficiency of PSII photochemistry (Fv/Fm), the traditional fluorescence induction kinetics (OIP) and the polyphasic fluorescence induction kinetics (OJIP), suggesting that water stress had no direct effects on the primary PSII photochemistry in dark-adapted leaves. However, PSII photochemistry in light-adapted leaves was modified in water-stressed plants. This was shown by the decrease in the actual PSII efficiency (ΦPSII), the efficiency of excitation energy capture by open PSII centres (Fv′/Fm′), and photochemical quenching (qP), as well as a significant increase in non-photochemical quenching (NPQ) in particular at high PFDs. In addition, photoinhibition and the xanthophyll cycle were investigated in water-stressed leaves when exposed to 50% full sunlight and full sunlight. At midday, water stress induced a substantial decrease in Fv/Fm which was reversible. Such a decrease was greater at higher irradiance. Similar results were observed in ΦPSII, qP, and Fv′/Fm′. On the other hand, water stress induced a significant increase in NPQ and the level of zeaxanthin via the de-epoxidation of violaxanthin and their increases were greater at higher irradiance. The results suggest that water stress led to increased susceptibility to photoinhibition which was attributed to a photoprotective process but not to a photodamage process. Such a photoprotection was associated with the enhanced formation of zeaxanthin via de-epoxidation of violaxanthin. The results also suggest that thermal dissipation of excess energy associated with the xanthophyll cycle may be an important adaptive mechanism to help protect the photosynthetic apparatus from photoinhibitory damage for CAM plants normally growing in arid and semi-arid areas where they are subjected to a combination of water stress and high light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2003.00061.x
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