Broadley Sarah L, Vondrak Tomas, Plane John M C
School of Chemistry, University of Leeds, Leeds, UK.
Phys Chem Chem Phys. 2007 Aug 21;9(31):4357-69. doi: 10.1039/b704920j. Epub 2007 Jun 12.
The reactions between Ca(+)(4(2)S(1/2)) and O(3), O(2), N(2), CO(2) and H(2)O were studied using two techniques: the pulsed laser photo-dissociation at 193 nm of an organo-calcium vapour, followed by time-resolved laser-induced fluorescence spectroscopy of Ca(+) at 393.37 nm (Ca(+)(4(2)P(3/2)-4(2)S(1/2))); and the pulsed laser ablation at 532 nm of a calcite target in a fast flow tube, followed by mass spectrometric detection of Ca(+). The rate coefficient for the reaction with O(3) is essentially independent of temperature, k(189-312 K) = (3.9 +/- 1.2) x 10(-10) cm(3) molecule(-1) s(-1), and is about 35% of the Langevin capture frequency. One reason for this is that there is a lack of correlation between the reactant and product potential energy surfaces for near coplanar collisions. The recombination reactions of Ca(+) with O(2), CO(2) and H(2)O were found to be in the fall-off region over the experimental pressure range (1-80 Torr). The data were fitted by RRKM theory combined with quantum calculations on CaO(2)(+), Ca(+).CO(2) and Ca(+).H(2)O, yielding the following results with He as third body when extrapolated from 10(-3)-10(3) Torr and a temperature range of 100-1500 K. For Ca(+) + O(2): log(10)(k(rec,0)/cm(6) molecule(-2) s(-1)) = -26.16 - 1.113log(10)T- 0.056log(10)(2)T, k(rec,infinity) = 1.4 x 10(-10) cm(3) molecule(-1) s(-1), F(c) = 0.56. For Ca(+) + CO(2): log(10)(k(rec,0)/ cm(6) molecule(-2) s(-1)) = -27.94 + 2.204log(10)T- 1.124log(10)(2)T, k(rec,infinity) = 3.5 x 10(-11) cm(3) molecule(-1) s(-1), F(c) = 0.60. For Ca(+) + H(2)O: log(10)(k(rec,0)/ cm(6) molecule(-2) s(-1)) = -23.88 - 1.823log(10)T- 0.063log(10)(2)T, k(rec,infinity) = 7.3 x 10(-11)exp(830 J mol(-1)/RT) cm(3) molecule(-1) s(-1), F(c) = 0.50 (F(c) is the broadening factor). A classical trajectory analysis of the Ca(+) + CO(2) reaction is then used to investigate the small high pressure limiting rate coefficient, which is significantly below the Langevin capture frequency. Finally, the implications of these results for calcium chemistry in the mesosphere are discussed.
采用两种技术研究了Ca(+)(4(2)S(1/2))与O(3)、O(2)、N(2)、CO(2)和H(2)O之间的反应：一是用193nm激光脉冲光解有机钙蒸气，随后用393.37nm处Ca(+)的时间分辨激光诱导荧光光谱法（Ca(+)(4(2)P(3/2)-4(2)S(1/2))）；二是在快速流动管中用532nm激光脉冲烧蚀方解石靶，随后用质谱法检测Ca(+)。与O(3)反应的速率系数基本与温度无关，k(189 - 312K) = (3.9 ± 1.2)×10^(-10) cm³分子⁻¹ s⁻¹，约为朗之万捕获频率的35%。原因之一是近共面碰撞的反应物和产物势能面之间缺乏相关性。发现Ca(+)与O(2)、CO(2)和H(2)O的复合反应在实验压力范围（1 - 80托）内处于过渡区。数据通过RRKM理论结合对CaO(2)(+)、Ca(+).CO(2)和Ca(+).H(2)O的量子计算进行拟合，当从10⁻³ - 10³托外推且温度范围为100 - 1500K时，以He作为第三体得到以下结果。对于Ca(+) + O(2)：log₁₀(k(rec,0)/cm⁶分子⁻² s⁻¹) = -26.16 - 1.113log₁₀T - 0.056log₁₀²T，k(rec,∞) = 1.4×10⁻¹⁰ cm³分子⁻¹ s⁻¹，F(c) = 0.56。对于Ca(+) + CO(2)：log₁₀(k(rec,0)/ cm⁶分子⁻² s⁻¹) = -27.94 + 2.204log₁₀T - 1.124log₁₀²T，k(rec,∞) = 3.5×10⁻¹¹ cm³分子⁻¹ s⁻¹，F(c) = 0.60。对于Ca(+) + H(2)O：log₁₀(k(rec,0)/ cm⁶分子⁻² s⁻¹) = -23.88 - 1.823log₁₀T - 0.063log₁₀²T，k(rec,∞) = 7.3×10⁻¹¹exp(830 J mol⁻¹/RT) cm³分子⁻¹ s⁻¹，F(c) = 0.50（F(c)是展宽因子）。然后对Ca(+) + CO(2)反应进行经典轨迹分析，以研究小的高压极限速率系数，该系数明显低于朗之万捕获频率。最后，讨论了这些结果对中间层钙化学的意义。
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