Franck-Condon simulation of the photoelectron spectrum of AsF₂and the photodetachment spectrum of AsF₂⁻using ab initio calculations: Ionization energy and electron affinity of AsF₂

RCCSD(T) and/or CASSCF/MRCI calculations were carried out on the X2B1state of AsF2, the X1A1, ã3B1and Ã1B1states of AsF2+, and the X1A1state of AsF2−employing the fully-relativistic small-core effective core potential (ECP10MDF) for As and basis sets of up to augmented correlation-consistent polarized valence quintuple-zeta (aug-cc-pV5Z) quality. Minimum-energy geometrical parameters and relative electronic energies were evaluated, including contributions from extrapolation to the complete basis set limit and from outer core correlation of the As 3d10electrons. In addition, simplified, explicitly correlated RHF/UCCSD(T)-F12x calculations were also performed employing different atomic orbital basis sets, and associated complementary auxiliary and density-fitting basis sets. The best theoretical estimates of the adiabatic ionization energies (AIE0) of AsF2(X2B1) to the X1A1and ã3B1states of AsF2+, including corrections for zero-point vibrational energy (ΔZPE), are 9.099(8) and 13.290(22) eV respectively. The best estimated electron affinity (EA0) of AsF2is 1.182(16) eV, also including Δ(ZPE). These are currently the most reliable AIE0and EA0values for AsF2. Potential energy functions (PEFs) of the X2B1state of AsF2, the X1A1and ã3B1states of AsF2+and X1A1state of AsF2−were computed at RCCSD(T)/aug-cc-pV5Z, RCCSD(T)/aug-cc-pCV5Z and RHF/UCCSD(T)-F12a/aug-cc-pCVTZ levels. These PEFs were employed in variational calculations of anharmonic vibrational wavefunctions, which were then utilised to calculate Franck-Condon factors (FCFs), using a method which includes allowance for anharmonicity and Duschinsky rotation. The computed FCFs were used to simulate the first two bands in the photoelectron spectrum of AsF2and the first band in the photodetachment spectrum of AsF2−, both yet to be recorded. The simulated spectra obtained using different sets of PEFs were found to be almost identical, suggesting that the simplified explicitly correlated UCCSD(T)-F12x method with a relatively small basis set can be a reliable alternative to the conventional RCCSD(T) correlation methods with a relatively large basis set, but at a significantly lower cost.