Ozone photodissociation: isotopic and electronic branching ratios for symmetric and asymmetric isotopologues.
Ozone photodissociation: isotopic and electronic branching ratios for symmetric and asymmetric isotopologues.
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臭氧光解离：对称和不对称同位素体的同位素和电子分支比。
DOI：
10.1021/jp307195v
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
R. Jost
中科院分区：
文献类型：
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作者：
S. Ndengué;R. Schinke;F. Gatti;H. Meyer;R. Jost
我们提出了臭氧的各种电子和同位素光解通道之间分支比率的新计算。特别强调同位素/同位素差异，因为臭氧光解作用对氧同位素和臭氧同位素富集或分馏的贡献对大气应用很重要。这些分支比依赖于光子能量，已经用一种全量子力学波包传播方法计算出来：多构型时变哈特里（MCTDH）方法。考虑了五种臭氧同位素：三种对称的，（16）O(3)（注666），（16）O(17)O(16)O（676）和（16）O(18)O(16)O (686)；两种不对称，（16）O(2)(17)O（注667）和（16）O(2)(18)O（668）。668和667的不对称同位素可以分解成66 + 8或68 + 6,668的不对称同位素可以分解成66 + 7或67 + 6。在Chappuis和Hartley带范围内，解离非常快，并且通过垂直于A (1)B(1) （Chappuis）和b3 (1)A’（Hartley/Huggins）电子态势能面（PESs）的复合吸收电位（CAPs）从波包通量中获得电子和同位素分支比。在哈金斯带范围内，667和668不对称同位素（如668→66 + 8或86 + 6）的同位素分支比是由C(s)对称的两个异构体的一个或另一个的选择性激发所对应的两个部分吸收截面的比值得到的，这两个异构体分别解离成66 + 8和86 + 6。我们发现668不对称同位素体的光解作用倾向于68 + 6通道，其倾向性随光子能量的变化在52% （Hartley）和54% （Huggins）之间变化。与单线态通道(O(3) + hυ→O((1)D) + O（2)（(1)Δ））的电子分支比在≈32,000 cm（-1）以上均接近90%。在此能量以下，单线态通道是能量封闭的，只有三重态通道(O(3) + hυ→O((3)P) + O（2)（(3)Σ））是开放的。需要这些分支比率来计算每种臭氧同位素物的光解速率，这反过来又有助于大气中原子氧和臭氧同位素的富集。
We present new calculations of the branching ratios between the various electronic and isotopic photodissociation channels of ozone. Special emphasis is placed on the isotopic/isotopologue differences because the contribution of the ozone photodissociation to the oxygen isotope and ozone isotopologue enrichments or fractionations is important for atmospheric applications. These branching ratios, which depend on photon energy, have been calculated with a full quantum mechanical wavepacket propagation approach: the multiconfiguration time-dependent Hartree (MCTDH) method. Five ozone isotopologues are considered: three symmetric, (16)O(3) (noted 666), (16)O(17)O(16)O (676), and (16)O(18)O(16)O (686); two asymmetric, (16)O(2)(17)O (noted 667) and (16)O(2)(18)O (668). The 668 and 667 asymmetric isotopologues can dissociate into either 66 + 8 or 68 + 6 for 668 and into 66 + 7 or 67 + 6 for 667. In the ranges of the Chappuis and Hartley bands, the dissociation is very fast and electronic and isotopic branching ratios are obtained from the wavepacket fluxes through complex absorbing potentials (CAPs) located perpendicular to the dissociation channels of the potential energy surfaces (PESs) of the A (1)B(1) (Chappuis) and B 3(1)A' (Hartley/Huggins) electronic states. In the range of the Huggins band the dissociation is much slower and the isotopic branching ratios of 667 and 668 asymmetric isotopologues, (e.g; 668 → 66 + 8 or 86 + 6) are obtained from the ratios of two partial absorption cross sections corresponding to the selective excitation of one or the other of the two isomers of C(s) symmetry, which dissociate respectively into 66 + 8 and 86 + 6. We find that the photodissociation of the 668 asymmetric isotopologue favors the 68 + 6 channel with a propensity varying between 52% (Hartley) and 54% (Huggins) as a function of the photon energy. The electronic branching ratios to the singlet channel (O(3) + hυ → O((1)D) + O(2)((1)Δ)) are all close to 90% above ≈32,000 cm(-1). Below this energy, the singlet channel is energetically closed and only the triplet channel (O(3) + hυ → O((3)P) + O(2)((3)Σ)) is open. These branching ratios are required to calculate the photolysis rates of each ozone isotopologue, which in turn contribute to the atomic oxygen and the ozone isotopic enrichments in the atmosphere.