Laboratory study of the reactions Mg + O3 and MgO + O3. Implications for the chemistry of magnesium in the upper atmosphere
Laboratory study of the reactions Mg + O3 and MgO + O3. Implications for the chemistry of magnesium in the upper atmosphere
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Mg O3 和 MgO O3 反应的实验室研究。
DOI：
10.1039/fd9950000411
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发表时间：
1995
影响因子：
3.4
通讯作者：
M. Helmer
中科院分区：
文献类型：
--
作者：
J. Plane;M. Helmer
在过量的O3和N2浴气中，利用193.3nm的脉冲光解离乙酰丙酮镁[Mg（C5 H7 O2）2]蒸气产生Mg原子，然后利用285.2nm的时间分辨激光诱导荧光（LIF）光谱研究了Mg + O3→ MgO + O2反应[Mg（31 P1- 31 S 0）]。由此得到的速率系数以阿克里尼乌斯形式给出：k（196 < T/K < 368）=（2.28 ± 0.74）× 10-10 exp[-（139 ± 84 K）/T] cm 3 molecule-1 s-1。因此，该反应是65至95公里大气中原子镁最快速的氧化过程。利用时间分辨激光诱导荧光（LIF）技术研究了MgO + O3→ MgO 2 + O2的反应过程，在499.4 nm处激发MgO（B 1 +-X1+，Δv= 0）跃迁，在600 nm以上监测MgO（B 1 +-A1+，Δv = 0）跃迁的发射.由此得到k（217 < T < 366 K）=（2.19 ± 1.8）× 10-10 exp[-（548 ± 271 K）/T] cm 3 molecule-1 s-1。量子计算表明，镁在高层大气中最稳定的形式是Mg（OH）2，它是由MgO和H2O之间的快速复合反应形成的。利用85 km以上观测到的Mg+剖面，建立了镁的一维模型，用以约束化学反应方案和金属的流星输入通量。原子Mg层预计将出现在与Na层相同的高度（约200米）。90公里），但峰值浓度较小的一个因素约。5.该模型表明，流星消融产生的Mg/Na通量之比约为0.5。这有力地证明，流星体的现有质量不会完全消融，残余部分富含镁。
The reaction Mg + O3→ MgO + O2 has been studied by the pulsed photodissociation at 193.3 nm of magnesium acetyl acetonate [Mg(C5H7O2)2] vapour to produce Mg atoms in an excess of O3 and N2 bath gas, followed by time-resolved laser-induced fluorescence (LIF) spectroscopy of atomic Mg at 285.2 nm [Mg(31 P1–31S0)]. The resulting rate coefficient is given in the Arrhenius form by k(196 < T/K < 368)=(2.28 ± 0.74)× 10–10 exp[–(139 ± 84 K)/T] cm3 molecule–1 s–1. This reaction is therefore the most rapid oxidation process of atomic Mg in the atmosphere between 65 and 95 km. The reaction MgO + O3→ MgO2+ O2 was investigated by the pulsed photodissociation of MgO3 coupled with time-resolved LIF by pumping the MgO(B 1Σ+–X 1Σ+, Δv= 0) transition at 499.4 nm and monitoring emission from the MgO(B 1Σ+–A 1Σ+, Δv⩽ 0) transition at wavelengths greater than 600 nm. This yields k(217 < T < 366 K)=(2.19 ± 1.8)× 10–10 exp[–(548 ± 271 K)/T] cm3 molecule–1 s–1. Ab initio quantum calculations were used to show that the most stable form of magnesium in the upper atmosphere is Mg(OH)2, formed from a rapid recombination reaction between MgO and H2O. A one-dimensional (1D) model of magnesium was then constructed by using observed Mg+ profiles above 85 km to constrain both the chemical reaction scheme and the meteoric input flux of the metal. The atomic Mg layer is predicted to occur at the same height as the Na layer (ca. 90 km), but with a peak concentration that is smaller by a factor of ca. 5. The model indicates that the ratio of the Mg/Na flux from meteoric ablation is about 0.5. This is strong evidence that the available mass of meteoroids does not ablate completely and that the residual fraction is enriched in magnesium.