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Abstract

Ab initio calculations employing effective core potentials and polarized triple‐zeta basis sets have been carried out for XeF₄ at the following levels: self‐consistent‐field (SCF) theory, Mller–Plesset second‐order perturbation theory (MP2), and coupled clustertheory with single and double excitations and a perturbational treatment of triple excitations (CCSD(T)). Pronounced correlation effects are found, especially for the Xe–F bond length and the vibrational frequencies. The theoretical predictions for the harmonic and anharmonic force fields and the associated spectroscopic constants have guided the analysis of the experimental data. Fourier transforminfrared spectra of monoisotopic ¹³⁶XeF₄ have been recorded between 100–1170 cm⁻¹ with an effective resolution of 0.002–0.004 cm⁻¹, and a rotational analysis has been performed for the ν₂ band. The high resolution results provide accurate molecular parameters for the ground state and the v₂=1 excited state of XeF₄ and allow a precise determination of the ground state Xe–F bond length, r₀=193.487(3) pm. The agreement between the experimental and the correlated theoretical results is generally quite good.