AB-INITIO MOLECULAR-ORBITAL STUDY OF THE TRICHLORINE RADICAL, CL-3

We report a rigorous ab initio study of the ground and low-lying excit ed-state potential-energy surfaces (PESs) of the Cl-2 radical at CASSC F, CASPT2, and MRSDCI levels of theory. The ground state has two Cl .. . Cl-2 van der Waals complexes, (X) over tilde L and (X) over tilde'B. The linear asymmetric minimum ((X) over tilde L) is (II)-I-2, with a Cl-Cl distance r = 3.90 bohr, and a Cl-M (M: the Cl-2 center-of-mass) distance R = 8.70 bohr. The bent asymmetric minimum ((X) over tilde'B) is of (2)A' symmetry, with r = 3.90 bohr, R = 6.85 bohr, and the angl e between (r) over cap and (R) over cap, gamma = 68.4 degrees. Spin-or bit CI (configuration interaction) predicts that the global minimum is linear (X) over tilde L ((II3/2)-I-2) with a bond dissociation energy of D-e(Cl-2((X) over tilde)-Cl) of 280 cm(-1). Low-lying doublet exci ted states have only one strongly bound structure, a linear symmetric (A) over tilde L (1 (IIg)-I-2) state with a bond distance of 4.67 bohr . This state is bound by similar to 4300cm(-1) with respect to the Cl- 2((II3/2)-I-3)+Cl asymptote, and its minimum lies about 8700 cm(-1) ab ove the (X) over tilde L van der Waals minimum. Transition dipole mome nt calculations show that the (A) over tilde-(X) over tilde transition is fully allowed. Two bound quartet minima were located. The most dee ply bound was QD3h (1 (4)A(1)') With a D-3h equilibrium geometry (r = 5.00 bohr) about 11 300 cm(-1) above (X) over tilde L. The other state , QC2v (1 (4)A(2)) had a C-2v equilibrium geometry (r(1) = 4.83 bohr a nd theta = 101.7 degrees) and an energy of about 13 500 cm(-1) relativ e to (X) over tilde L. Although Cl-3((X) over tilde) is shown to be un stable, the present results support the notion that Cl-3 participates in Cl atom recombination processes. However, the energies and transiti on moments of the low-lying excited states are not consistent with ele ctronic spectra that have been tentatively assigned to Cl-3. (C) 1998 American Institute of Physics.