Arulmozhiraja Sundaram, Ehara Masahiro, Nakatsuji Hiroshi
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyou-ku, Kyoto 615-8510, Japan.
J Chem Phys. 2007 Jan 28;126(4):044306. doi: 10.1063/1.2428296.
Several lowest-lying singlet electronic states of vinyl fluoride, trans-, cis-, and 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene were investigated by using symmetry-adapted cluster configuration interaction theory. Basis sets up to Dunning's aug-cc-pVTZ augmented with appropriate Rydberg functions were utilized for the calculations. Calculated excitation energies show a good agreement with the available experimental values. Even in the troublesome pi-->pi() transitions, the excitation energies obtained in the present study agree well with the experimental values except in one or two fluoroethylenes. Strong mixing between different states was noticed in a few fluoroethylenes; especially the mixing is very strong between pi-pi() and pi-3ppi states in trifluoroethylene. No pure pi-sigma() excited state was found in almost all the fluoroethylenes. Several assignments and reassignments of features in the experimental spectra were suggested. The present study does not support the existing argument that the interaction between the pi-pi() and sigma-sigma() states is the reason behind the blueshift of around 1.25 eV in the pi-pi() excitation energy of tetrafluoroethylene. Possible reasons, including structural changes, for this shift are discussed in detail. Several low-lying triplet excited states were also studied.
利用对称适配团簇组态相互作用理论研究了氟乙烯、反式、顺式和1,1 - 二氟乙烯、三氟乙烯以及四氟乙烯的几个最低单重态电子态。计算中使用了高达邓宁的aug-cc-pVTZ并附加适当里德堡函数的基组。计算得到的激发能与现有的实验值吻合良好。即使在棘手的π→π跃迁中，本研究得到的激发能除了在一两种氟乙烯中之外，与实验值也吻合得很好。在一些氟乙烯中注意到不同态之间有强烈混合；特别是在三氟乙烯中，π - π态和π - 3ππ态之间的混合非常强烈。几乎在所有氟乙烯中都未发现纯的π - σ激发态。对实验光谱中的特征进行了一些归属和重新归属。本研究不支持现有的观点，即π - π态和σ - σ态之间的相互作用是四氟乙烯π - π激发能中约1.25 eV蓝移的原因。详细讨论了包括结构变化在内的这种蓝移的可能原因。还研究了几个低激发三重态。
