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Abstract

Fourier transform infrared spectra of KrF₂, XeF₂, and monoisotopic ¹³⁶XeF₂ have been recorded in the ν₃ and ν₁ + ν₃ ranges with an effective resolution of 0.003–0.007 cm⁻¹. About 10 000 rovibrational lines belonging to cold bands and to hot bands with ν₁, ν₂, 2ν₂, and ν₃ as lower levels have been assigned and fitted. The high‐resolution results from this work and from two previous studies provide a rather complete set of precise spectroscopic constants and accurate ground‐state and equilibrium geometries for both molecules. In the case of ⁸⁴KrF₂, r₀ = 188.2821(9) pm supersedes previous incorrect r₀ values, and r_e =187.6930(23) pm represents the first determination of the Kr–F equilibrium distance. Ab initio calculations employing effective core potentials and polarized double‐zeta basis sets have been carried out at the following levels: self‐consistent‐field (SCF) theory, the Møller–Plesset second order perturbation theory (MP2), and coupled clustertheory with single and double excitations (CCSD) and a perturbational treatment of triple excitations (CCSD(T)). Pronounced correlation effects are found, especially for KrF₂. The agreement between the correlated theoretical and the experimental results is generally quite good. A theoretical analysis clarifies the origin of the positive α₂ vibration–rotation coupling constants which have been observed for the bending vibrations in both molecules. Reliable harmonic and anharmonic force fields are presented for KrF₂ and XeF₂.