The singlet-triplet separation in CF2:: State-of-the-art ab initio calculations and Franck-Condon simulations including anharmonicity

Geometrical parameters, vibrational frequencies and relative electronic energies of the (XB1)-B-2, state of CF2- and the X(1)A(1), and a(3)B(1), states of CF2 have been calculated. Core-electron effects on the computed minimum-energy geometries and relative electronic energies have been investigated, and relativistic contributions to the computed relative electronic energies calculated. Potential energy functions of the x(2)B(1) state of CF2- and the X(1)A(1) and a(3)B(1) states of CF2 hove been determined, and anhormonic vibrational wavefunctions of these states calculated variationally. Franck-Condon factors including onharmonicity and Duschinsky rotation have been computed and used to simulate the 64 emission spectrum of CF2 determined by S. Kodo [Chem. Phys. Lett. 1978, 55, 353] and the 364 nm laser photodetachment spectrum of CF2- obtained by R. L. Schwartz et al. [J. Phys. Chem. A 1999, 103, 8273]. Comparison between theory and experiment shows that the theoretical approach benchmarked in the present study is able to give highly reliable positions for the CF2(X(1)A(1))+ e <- CF2-((XB1)-B-2) and CF2 (a(3)B(1))+e <- CF2-((XB1)-B-2) bands in the photoelectron spectrum of CF2- and a reliable singlet-triplet gap for CF2. It is therefore concluded that the some theoretical approach should give reliable simulated CCl2(X(1)A(1))+e <- CCl2-((XB1)-B-2) and CCl2(a(3)B(1))+e <- CCl2-((XB1)-B-2) bands in the photodetochment spectrum of CCl2- and a reliable singlet-triplet gap for CCl2.