The X̃²Bi, òB₂, B̃²A₁, and C̃²A₂states of Cl₂O⁺: Ab initio calculations and simulations of the he I photoelectron spectrum

CASSCF and QCISD calculations were carried out on the X̃1A1state of Cl2O and the X̃2B1, Ã2B2, B̃2A1, and C̃2A2states of Cl2O+in order to obtain their minimum-energy geometries and harmonic vibrational frequencies. Cl2O+← Cl2O X̃1A1vertical 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 C̃2A2cationic states. The adiabatic ionization energy position and the vibrational assignments of the Cl2O+Ã2B2← Cl2O X̃1A1band were revised, based on spectral simulations, which included "hot" bands.