Ab initio calculations on SF_2 and its low-lying cationic states:Anharmonic Franck-Condon simulation of the uv photoelectron spectrum of SF_2

摘要

Geometry optimization calculations were carried out on the X ~1A_1 state of SF_2 and the X ~2B_1,A ~2A_1, B~2B_2,C~2B_2,D~2A_1,and E ~2A_2 states of SF_2~+ employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality.Effects of core electron(S 2s~22p~6 and F 1s~2 electrons)correlation and basis set extension to the complete basis set limit on the computed minimum-energy geometries and relative electronic energies(adiabatic and vertical ionization energies)were investigated.RCCSD(T)potential energy functions(PEFs) were calculated for the X ~1A_1 state of SF_2 and the low-lying states of SF_2 listed above employing the aug-cc-pV(5 + d)Z and aug-cc-pV5Z basis sets for S and F,respectively.Anharmonic vibrational wave functions of these neutral and cationic states of SF_2,and Franck-Condon(FC)factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)PEFs.Calculated FC factors with allowance for Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron bands of SF_2.The agreement between the simulated and observed first bands in the He I photoelectron spectrum reported by de Leeuw et al. [Chem.Phys.34,287(1978)] is excellent.Our calculations largely support assignments made by de Leeuw et al.on the higher ionization energy bands of SF_2.