Ab initio molecular-orbital study of the trichlorine radical, Cl3

We report a rigorous ab initio study of the ground and low-lying excited-state potential-energy surfaces (PESs) of the Cl3 radical at CASSCF, CASPT2, and MRSDCI levels of theory. The ground state has two Cl⋯Cl2 van der Waals complexes, XL and X′B. The linear asymmetric minimum (XL) is 2Π, with a Cl–Cl distance r=3.90 bohr, and a Cl–M (M: the Cl2 center-of-mass) distance R=8.70 bohr. The bent asymmetric minimum (X′B) is of 2A′ symmetry, with r=3.90 bohr, R=6.85 bohr, and the angle between r and R, γ=68.4°. Spin–orbit CI (configuration interaction) predicts that the global minimum is linear XL (2Π3/2) with a bond dissociation energy of De(Cl2(X)-Cl) of 280 cm−1. Low-lying doublet excited states have only one strongly bound structure, a linear symmetric AL (1 2Πg) state with a bond distance of 4.67 bohr. This state is bound by ∼4300 cm−1 with respect to the Cl2(3Πu)+Cl asymptote, and its minimum lies about 8700 cm−1 above the XL van der Waals minimum. Transition dipole moment calculations show that t...

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