Theoretical study of the fast photodissociation channels of the monohalobenzenes
Theoretical study of the fast photodissociation channels of the monohalobenzenes
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DOI：
10.1021/jp0379648
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发表时间：
2004-03-25
影响因子：
2.9
通讯作者：
Lunell, S
中科院分区：
文献类型：
--
作者：
Liu, YJ;Persson, P;Lunell, S
用多参比CASSCF和CASPT 2方法对氟苯、氯苯、溴苯和碘苯的激发态性质进行了理论研究。在实验上，氯苯和溴苯已知表现出一个快速解离通道，而碘苯表现出两个快速解离通道。计算表明，氯苯，溴苯，和较慢的碘苯解离通道是由于从绑定（π，π *）单重激发态的排斥（n，σ *）三重激发态的系统间交叉。更快的碘苯解离通道，而不是发现由一个反键（n，σ *）单重激发态的直接解离。CASPT2计算预测氟苯光解离的开始应该发生在196 nm附近，单个时间常数长于1 ns。CASSCF几何形状和准确的MSCASPT2计算的垂直激发能的基态以及第一激发单重态和三重态的所有一卤代苯。
Excited state properties of fluorobenzene, chlorobenzene, bromobenzene, and iodobenzene have been investigated theoretically using multireference CASSCF and CASPT2 methods. Experimentally, chlorobenzene and bromobenzene are known to exhibit one fast dissociation channel, whereas iodobenzene exhibits two fast dissociation channels. The calculations indicate that the chlorobenzene, the bromobenzene, and the slower iodobenzene dissociation channels are due to intersystem crossings from a bound (pi,pi*) singlet excited state to a repulsive (n,sigma*) triplet excited state. The faster iodobenzene dissociation channel is instead found to be caused by a direct dissociation of an antibonding (n,sigma*) singlet excited state. The CASPT2 calculations predict that the onset of fluorobenzene photodissociation should occur around 196 nm, with a single time constant longer than 1 ns. CASSCF geometries and accurate MSCASPT2 calculated vertical excitation energies are presented for the ground state as well as the first excited singlet and triplet states of all the monohalobenzenes.