title: The singlet-triplet separation in CF2: state-of-the-art ab initio calculations and Franck-Condon simulations including anharmonicity.
abstract: Geometrical parameters, vibrational frequencies and relative electronic energies of the X2B1 state of CF2- and the X1A1 and ã3B1 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 X2B1 state of CF2- and the X1A1 and ã3B1 states of CF2 have been determined, and anharmonic vibrational wavefunctions of these states calculated variationally. Franck-Condon factors including anharmonicity and Duschinsky rotation have been computed and used to simulate the ã-X emission spectrum of CF2 determined by S. Koda [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, 8213]. 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(X1A1) + e <-- CF2-(X2B1) and CF2(ã3B1) + e <-- CF2-(X2B1) bands in the photoelectron spectrum of CF2- and a reliable singlet-triplet gap for CF2. It is therefore concluded that the same theoretical approach should give reliable simulated CCl2(X1A1) + e <-- CCl2-(X2B1) and CCl2(ã3B1) + e <-- CCl2-(X2B1) bands in the photodetachment spectrum of CCl2- and a reliable singlet-triplet gap for CCl2.
authors.affiliation: Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hung Hom, Hong Kong. bcftchau@inet.polyu.edu.hk
authors.forename: Foo-tim
authors.initials: FT
authors.lastname: Chau
authors.forename: Daniel K W
authors.initials: DK
authors.lastname: Mok
authors.forename: Edmond P F
authors.initials: EP
authors.lastname: Lee
authors.forename: John M
authors.initials: JM
authors.lastname: Dyke