CASSCF and CASPT2 study on O- and Cl-loss predissociation mechanisms of OClO (A(2)A2).
CASSCF and CASPT2 study on O- and Cl-loss predissociation mechanisms of OClO (A(2)A2).
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DOI：
10.1021/jp110894v
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发表时间：
2011-03
期刊：
影响因子：
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通讯作者：
Qingyong Meng;Ming-Bao Huang
中科院分区：
文献类型：
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作者：
Qingyong Meng;Ming-Bao Huang
为了研究OClO（A（2）A（2））的失氧和失氯预解离机制，我们在CASPT ~ 2水平上计算了几个低激发态的O和Cl失解离势能曲线（绝热最小能量解离路径），并在CASPT ~ 2和CASSCF水平上定位了多对势能面的最小能量交叉点（MECP）。根据我们的计算结果（包括MECPs上的自旋-轨道耦合），我们预测了A（2）A（2）的三个O-损失预解离过程和四个Cl-损失预解离过程.最有利的失氧预解离过程为OClO（A（2）A（2））→ A（2）A（2）/1（2）B（2）MECP → 1（2）B（2）（1（2）A '）→ O（（3）P（g））+ ClO（X（2）O）（第一失氧极限），该过程所需能量为2.92eV。最佳失Cl预解离过程为OClO（A（2）A（2））→ A（2）A（2）/1（2）B（2）MECP → TS 1（1（2）B（2））→ 1（2）B（2）/1（2）A（1）MECP → Cl（（2）P（u））+ O（2）（X（3）P（g）（-）（第一极限），所需能量为3.08 eV。在先前提出的机制（过程）中，A（2）A（2）状态被认为是通过1（2）A（1）（A（2）A（2）→ 1（2）A（1）→ 1（2）B（2））进入重要的1（2）B（2）状态。我们发现A（2）A（2）态可以直接跃迁到1（2）B（2）（在A（2）A（2）/1（2）B（2）MECP处，CASPT 2能量（相对于X（2）B（1））和CASSCF自旋轨道耦合分别为2.92 eV和61.3 cm（-1））。我们比较了我们的过程（A（2）A（2）→ 1（2）B（2）→.）用过程（A（2）A（2）→ 1（2）A（1）→ 1（2）B（2）→.）建议在以前的MRCI研究和重写我们使用我们的计算结果。从能量上讲，O-损失预解离（到第一极限）的MRCI过程仅比我们的过程稍微有利（0.13 eV），而Cl-损失预解离（到第一和第二极限）的MRCI过程需要与我们的过程相同的能量。通过考虑无辐射跃迁的概率，MRCI过程不如我们的过程有利，因为MRCI过程通过更多的PES/PES交叉（更多的MECP）进行。解释了有关光解离的实验事实。
For studying O- and Cl-loss predissociation mechanisms of OClO (A(2)A(2)), we calculated O- and Cl-loss dissociation potential energy curves (adiabatic minimum-energy dissociation paths) of several low-lying doublet and quartet states at the CASPT2 level and located the MECPs (minimum energy crossing points) for many pairs of the potential energy surfaces (PESs) at the CASPT2 and CASSCF levels. On the basis of our calculation results (including the spin-orbit couplings at the MECPs), we predict three processes for O-loss predissociation of A(2)A(2) and four processes for Cl-loss predissociation of A(2)A(2). The most favorable process for O-loss predissociation is OClO (A(2)A(2)) → A(2)A(2)/1 (2)B(2) MECP → 1 (2)B(2) (1 (2)A') → O ((3)P(g)) + ClO (X(2)Π) (the first O-loss limit), and the needed energy for this process from X(2)B(1) is 2.92 eV. The most favorable process for Cl-loss predissociation is OClO (A(2)A(2)) → A(2)A(2)/1 (2)B(2) MECP → TS1 (1 (2)B(2)) → 1 (2)B(2)/1 (2)A(1) MECP → Cl ((2)P(u)) + O(2) (X(3)Σ(g)(-)) (the first limit), and the needed energy is 3.08 eV. In the previously suggested mechanisms (processes), the A(2)A(2) state was considered to go to the important 1 (2)B(2) state via 1 (2)A(1) (A(2)A(2) → 1 (2)A(1) → 1 (2)B(2)). In the present study we have found that the A(2)A(2) state can directly go to 1 (2)B(2) (at the located A(2)A(2)/1 (2)B(2) MECP the CASPT2 energy (relative to X(2)B(1)) and CASSCF spin-orbit coupling are 2.92 eV and 61.3 cm(-1), respectively). We have compared our processes (A(2)A(2) → 1 (2)B(2) → ...) with the processes (A(2)A(2) → 1 (2)A(1) → 1 (2)B(2) → ...) suggested in the previous MRCI studies and rewritten by us using our calculation results. Energetically the MRCI process for O-loss predissociation (to the first limit) is only slightly (0.13 eV) more favorable than our process, and the MRCI processes for Cl-loss predissociation (to the first and second limits) need the same energies as our processes. By considering the probabilities of radiationless transitions, the MRCI processes are less favorable than our processes since the MRCI processes proceed via more PES/PES crossings (more MECPs). The experimental facts concerning the photodissociation are explained.