Ab initio calculations on SF2 and its low-lying cationic states: Anharmonic Franck-Condon simulation of the uv photoelectron spectrum of SF2

Abstract

states of SF 2 + employing the restricted-spin coupled-cluster single-double plus perturbative triple excitation ͓RCCSD͑T͔͒ method and basis sets of up to the augmented correlation-consistent polarized quintuple-zeta ͓aug-cc-pV͑5+d͒Z͔ quality. Effects of core electron ͑S 2s 2 2p 6 and F 1s 2 electrons͒ 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 energies͒ were investigated. RCCSD͑T͒ potential energy functions ͑PEFs͒ were calculated for the X 1 A 1 state of SF 2 and the low-lying states of SF 2 + listed above employing the aug-cc-pV͑5+d͒Z 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 ͑FC͒ factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD͑T͒ 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 ͑1978͔͒ is excellent. Our calculations largely support assignments made by de Leeuw et al. on the higher ionization energy bands of SF 2 .

Low-lying electronic states of SF2 and its ions as studied by the MRCI technique

“…In agreement with the results of Lee et al [9] obtained recently for SF 2 and SF þ 2 , an inclusion of the core electron correlation was found to have only a small (up to 0.07 eV) effect upon the excitation energies.…”

“…Previous experimental and theoretical work on SF þ 2 was most recently summarized by Lee et al [9]. Also in Ref.…”

“…Both sets of calculated results compare favorably with the available experimental values of VIE (Table 2). The major goal of the high-level calculations by Lee et al [9] was to improve an understanding of the experimental He(I) photoelectron spectrum of SF þ 2 . As a consequence, they primarily concentrated on the states which can be reliably described by taking into account a oneelectron excitation only.…”

“…[9], a careful investigation of the X 2 B 1 , 1 2 A 1 , 1 2 A 2 , 1 2 B 2 , 2 2 A 1 and 2 2 B 2 electronic states of SF þ 2 was presented. Table 2 shows our geometries, excitation energies and vertical ionization energies (VIE) together with the RCCSD(T) results obtained using huge basis sets [9]. It also contains the experimental values of VIE [10].…”

“…Section 2) they were compared to the MRCI results of Liu and Huang [7] and, whenever possible, to experiment [8]. Second, owing to an excellent agreement between these data and our results (see Section 3.1), we applied the MRCI/CBS//MRCI/aug-cc-pVQZ approach to the X 2 B 1 , 1 2 A 1 , 1 2 A 2 , 1 2 B 2 , 2 2 A 1 and 2 2 B 2 states of SF þ 2 and compared the relevant parameters to the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] values of Lee et al [9] and to their experimental counterparts [10]. As the MRCI values again closely matched the reference data, we applied this strategy also to SF À 2 , which was previously studied only in its ground state.…”