The X̃²B₁, òB₂, B̃²A₁, and C̃²A₂ States of Cl₂O⁺:  ab Initio Calculations and Simulations of the He I Photoelectron Spectrum

Abstract

CASSCF and QCISD calculations were carried out on the X̃A1 state of Cl2O and the X̃B1, Ã2B2, B̃2A1, and C̃2A2 states of Cl2O+ in order to obtain their minimum-energy geometries and harmonic vibrational frequencies. Cl2O+ ← Cl2O X̃1A1 vertical and adiabatic ionization energies were also computed at the RCCSD(T)//QCISD level. Spectral simulations based on the ab initio results were performed for the first four bands of the He I photoelectron spectra of Cl2O. Iterative Franck−Condon analyses were also carried out. Comparison between the simulated and the observed spectra gave, for the first time, experimentally derived geometries, for the X̃2B1, Ã2B2, and C̃2A2 cationic states. The adiabatic ionization energy position and the vibrational assignments of the Cl2O+ Ã2B2 ← Cl2O X̃1A1 band were revised, based on spectral simulations, which included “hot” bands.

Potential energy functions of the X̃ 2B1, Ã 2B2, B̃ 2A1, and C̃ 2A2 states of Cl2O+ and the X̃ 1A1 state of Cl2O: Franck–Condon simulations of photoelectron bands of Cl2O which include anharmonicity

“…In summary, the four PE bands, which appear in the He I PE spectrum of Cl 2 photoelectron band: ͑a͒ using harmonic FCFs, the anharmonic IFCA geometry ͑1.697 Å; 90.92°͒ and the AIE value of 11.918 eV; ͑b͒ using harmonic FCFs, the QCISD/6-31G* geometry ͑1.726 Å; 94.84°from Ref. 2͒ and the AIE value of 11.918 eV; ͑c͒ using harmonic FCFs, the harmonic IFCA geometry ͑1.705 Å; 97.0°͒ and the AIE value of 12.071 eV; and ͑d͒ using anharmonic FCFs, the anharmonic IFCA geometry ͑1.697 Å; 90.92°͒ and the AIE value of 11.918 eV ͑same as Fig.…”

“…For the cationic states, the only available experimental geometrical parameters were derived from IFCA procedures carried out in our previous study, employing the harmonic oscillator model. 2 Revised IFCA geometrical parameters for each cationic state, obtained from the present study including anharmonicity, will be discussed later, when the simulated spectra are discussed below. In Table II, the computed fundamental frequencies of the symmetric stretching and bending modes obtained from the RCCSD͑T͒/aug-cc-pVQZ or CASSCF/MRCI/aug-ccpVQZ͑no g͒ PEFs are given together with the harmonic frequencies.…”

“…1͒ based on the harmonic oscillator model. 2 Subsequently, we published a combined experimental and computational study on the He I PE spectrum of F 2 O. 3 The ab initio part of the later study on F 2 O included energy scans on the symmetric stretching and bending surfaces, giving fitted potential energy functions ͑PEFs͒, which were employed in Franck-Condon factor ͑FCF͒ calculations which included the effects of anharmonicity.…”

“…1 In addition, the computed FCFs involving the asymmetric stretching mode, based on the harmonic oscillator model, have negligible relative intensities. 2 Terms of up to the fourth order and also the C 05 , C 06 , C 50 , and C 60 terms were included in the PEF ͓Eq. ͑1͔͒ for all states considered.…”

The X̃ 2B1, B22, A12, and A22 states of oxygen difluoride cation (F2O+): High-level ab initio calculations and simulation of the ultraviolet photoelectron spectrum of F2O

“…10,11,47,48 In the IFCA procedure, the geometry of the neutral molecule is fixed at the available experimental geometry, while the cationic state geometrical parameters are adjusted systematically ͑initially from the predicted ab initio geometry changes͒, until the simulated spectrum matches the experimental one. The IFCA procedure can be carried out with both the harmonic and AN-FCF method.…”