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 X̃2B1 state of CF2and the X̃1A1 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 X̃2B1 state of CF2and the X̃1A1 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–X̃ emission spectrum of CF2 determined by S. Koda [Chem. Phys. Lett. 1978, 55, 353] and the 364 nm laser photodetachment spectrum of CF2obtained 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(X̃1A1)+e←CF2(X̃2B1) and CF23B1)+e←CF2(X̃2B1) bands in the photoelectron spectrum of CF2and a reliable singlet–triplet gap for CF2. It is therefore concluded that the same theoretical approach should give reliable simulated CCl2(X̃1A1)+e←CCl2(X̃2B1) and CCl23B1)+e←CCl2(X̃2B1) bands in the photodetachment spectrum of CCl2and a reliable singlet–triplet gap for CCl2.