Amaro-Estrada J I, Ramírez-Solís A
Departamento de Física, Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Chamilpa, Cuernavaca, Morelos 62209, Mexico.
J Chem Phys. 2009 Sep 28;131(12):124308. doi: 10.1063/1.3239470.
The nine lowest-lying singlet and triplet (X (1)Sigma(+), 2 (1)Sigma(+), 3 (1)Sigma(+), (3)Sigma(+), 1 (3,1)Pi, 2 (3)Pi, and (3,1)Delta) electronic states of AgBr were studied through state-specific Complete Active Space Self-Consistent Field with 16 active electrons in 12 orbitals followed by extensive Averaged Coupled Pair Functional and CIPT2 calculations with large optimized valence basis sets. The spin-orbit effects were included to obtain the Omega fine-structure states arising from the |Lambda S Sigma> parents. Even before the inclusion of the spin-orbit effects, the 2 (1)Sigma(+) and 3 (1)Sigma(+) states present shallow minima near the equilibrium geometry of the ground state. The 2 (1)Sigma(+) state has another minimum around 8.0 a.u. and is attractive up to 20 a.u. The lowest (3,1)Pi states were found to be totally repulsive while the (3,1)Delta states present deep minima around 4.8 a.u. Most of the calculated spectroscopic constants for the ground and B states are slightly improved with respect to the previous theoretical study using the much smaller CASSCF(16,10) reference wave functions [M. Guichemerre et al., Chem. Phys. 280, 71 (2002)]. The observed B<--X transition is confirmed as arising from the singlet-to-singlet 0(+)(2 (1)Sigma(+))<--0(+)(X (1)Sigma(+)) excitation around 31 900 cm(-1). However, at variance with the previous theoretical prediction, the C(Omega=0(+)) state is dominated around the equilibrium geometry of the ground state by the third (1)Sigma(+) state with a small contribution from the 2 (3)Pi state around 43,500 cm(-1); thus the X-C excitation is now explained as arising also from a singlet-to-singlet spin-allowed transition.
通过特定态的完全活性空间自洽场方法（在12个轨道中包含16个活性电子），随后使用大型优化价基组进行广泛的平均耦合对函数和CIPT2计算，研究了AgBr的九个最低单重态和三重态（X (1)Σ⁺、2 (1)Σ⁺、3 (1)Σ⁺、(3)Σ⁺、1 (3,1)Π、2 (3)Π和(3,1)Δ）电子态。考虑了自旋 - 轨道效应以获得由|Λ S Σ>母态产生的Ω精细结构态。甚至在考虑自旋 - 轨道效应之前，2 (1)Σ⁺和3 (1)Σ⁺态在基态平衡几何结构附近呈现出浅的极小值。2 (1)Σ⁺态在约8.0 a.u.处有另一个极小值，并且在高达20 a.u.时具有吸引力。发现最低的(3,1)Π态完全是排斥的，而(3,1)Δ态在约4.8 a.u.处呈现出深的极小值。与之前使用小得多的CASSCF(16,10)参考波函数的理论研究相比[M. Guichemerre等人，《化学物理》280, 71 (2002)]，基态和B态的大多数计算光谱常数略有改进。观察到的B←X跃迁被确认为源于单重态到单重态0(+)(2 (1)Σ⁺)←0(+)(X (1)Σ⁺)激发，约为31900 cm⁻¹。然而，与之前的理论预测不同，在基态平衡几何结构附近，C(Ω = 0(+))态由第三个(1)Σ⁺态主导，2 (3)Π态在约43500 cm⁻¹处有小的贡献；因此，现在将X - C激发解释为也源于单重态到单重态的自旋允许跃迁。
