Yamashita Takefumi, Kato Shigeki
Department of Chemistry, Graduate School of Science, Kyoto University, 606-8502, Japan.
J Chem Phys. 2004 Aug 1;121(5):2105-16. doi: 10.1063/1.1768158.
A set of analytical potential energy surfaces (PESs) for six singlet excited states of NOCl are constructed based on multireference configuration interaction calculations. The total absorption cross section at the energy range of 2-7 eV is calculated by quantum dynamics calculations with the present PESs and transition dipole moments. The calculated absorption spectrum agrees well with the experiment. It is also found that the A band with the absorption maximum at 6.3 eV is attributed to the transition to the 4 1A' state, though the excitations to the 3 1A' and 3 1A" states contribute to the spectrum at the energy range between 4 and 5 eV. The spin-forbidden transitions are concluded to be negligibly weak. The mechanism of photodissociation reaction at the energy region corresponding to the A band is examined. The nonadiabatic transition rates from the 4 1A' state to lower singlet and triplet states are estimated by Fermi's golden rule, and the transitions to the 1 1A' and 3 1A' states induced by vibronic coupling are found to be the predominant dissociation pathways. The experimentally observed energy dependence of the recoil anisotropy of the fragments is discussed based on the calculated nonadiabatic transition rates.
基于多参考组态相互作用计算，构建了NOCl六个单重激发态的一组分析势能面（PESs）。利用当前的PESs和跃迁偶极矩，通过量子动力学计算得到了2-7 eV能量范围内的总吸收截面。计算得到的吸收光谱与实验结果吻合良好。还发现，在6.3 eV处具有吸收最大值的A带归因于向4 1A'态的跃迁，尽管向3 1A'和3 1A''态的激发在4-5 eV的能量范围内对光谱有贡献。自旋禁戒跃迁被认为弱到可以忽略不计。研究了与A带对应的能量区域内光解离反应的机制。通过费米黄金规则估计了从4 1A'态到较低单重态和三重态的非绝热跃迁速率，发现由振动耦合引起的向1 1A'和3 1A'态的跃迁是主要的解离途径。基于计算得到的非绝热跃迁速率，讨论了实验观察到的碎片反冲各向异性的能量依赖性。
