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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 re =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.
