Sobczyk Monika, Simons Jack
Chemistry Department and Henry Eyring Center for Theoretical Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
J Phys Chem B. 2006 Apr 13;110(14):7519-27. doi: 10.1021/jp0604701.
Ab initio electronic structure methods are used to estimate the cross sections for electron transfer from donor anions having electron binding energies ranging from 0.001 to 0.6 eV to each of three sites in a model disulfide-linked molecular cation. The three sites are (1) the S-S sigma() orbital to which electron attachment is rendered exothermic by Coulomb stabilization from the nearby positive site, (2) the ground Rydberg orbital of the -NH(3)(+) site, and (3) excited Rydberg orbitals of the same -NH(3)(+) site. It is found that attachment to the ground Rydberg orbital has a somewhat higher cross section than attachment to either the sigma orbital or the excited Rydberg orbital. However, it is through attachment either to the sigma() orbital or to certain excited Rydberg orbitals that cleavage of the S-S bond is most likely to occur. Attachment to the sigma() orbital causes prompt cleavage because the sigma energy surface is repulsive (except at very long range). Attachment to the ground or excited Rydberg state causes the S-S bond to rupture only once a through-bond electron transfer from the Rydberg orbital to the S-S sigma() orbital takes place. For the ground Rydberg state, this transfer requires surmounting an approximately 0.4 eV barrier that renders the S-S bond cleavage rate slow. However, for the excited Rydberg state, the intramolecular electron transfer has a much smaller barrier and is prompt.
从头算电子结构方法用于估算电子从电子结合能范围为0.001至0.6电子伏特的供体阴离子转移至模型二硫键连接的分子阳离子中三个位点的截面。这三个位点分别是：（1）S-S σ轨道，由于附近正位点的库仑稳定作用，电子附着于此轨道会放热；（2）-NH₃⁺位点的基态里德堡轨道；（3）同一-NH₃⁺位点的激发态里德堡轨道。研究发现，附着于基态里德堡轨道的截面略高于附着于σ轨道或激发态里德堡轨道的截面。然而，最有可能发生S-S键断裂的是通过附着于σ轨道或某些激发态里德堡轨道。附着于σ轨道会导致迅速断裂，因为σ能量表面是排斥性的（除了在非常长的距离）。附着于基态或激发态里德堡态只会在里德堡轨道到S-S σ轨道发生穿键电子转移后才导致S-S键断裂。对于基态里德堡态，这种转移需要克服约0.4电子伏特的势垒，这使得S-S键断裂速率较慢。然而，对于激发态里德堡态，分子内电子转移的势垒要小得多，且是迅速的。
