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
The harmonic and anharmonic force fields of the title compounds have been calculated at the ab initio self-consistent-field level using effective core potentials and polarized double-zeta basis sets. Additional calculations for PH2F employ larger basis sets and include electron correlation. Many rovibrational constants are predicted theoretically. The infrared spectra generated from the ab initio data have guided the experimental identification of PH2F and PH2Cl in the gas phase. High resolution Fourier transform infrared spectra of these unstable molecules have been recorded for the first time. Rotational analyses for several bands are reported which provide accurate ground state constants and a precise characterization of a number of vibrationally excited states. The accuracy of the ab initio predictions for PH2F and PH2Cl is evaluated by comparisons with these experimental data.
The harmonic and anharmonic force fields of PH3F2 have been calculated at the ab initio self‐consistent‐field level using polarized split‐valence and triple‐zeta basis sets. PH3F2 has been prepared in pure form and identified unambiguously in the gas phase by Doppler‐limited Fourier transform infrared spectroscopy. Guided by the theoretical predictions for the rotation–vibration spectra and the spectroscopic constants, the observed bands have been assigned and several of them rotationally analyzed, in particular ν4/2ν7±2, ν2 + ν4/ν2 + 2ν7±2, and ν5/ν3+ ν8. PH3F2 is found to have a D3h structure, ro (PH) = 1.394(4) Å and ro (PF) = 1.6468(2) Å. The theoretical results are in good agreement with experiment, both for the structure and for the available spectroscopic constants. The present study demonstrates the advantages of a combined theoretical and experimental approach to the spectroscopy of reactive molecules
The v8 band of CF2NH near 830 cm" 1 has been measured with a resolution of 0.003 cm" 1 and rotationally analyzed. The band is unperturbed, and its rovibrational parameters are given up to fourth order. Theoretical harmonic and anharmonic force constants have been calculated at the 6-31 G** SCF level, and all vibration-rotation interaction constants ctt and anharmonicity constants xu are predicted. The theoretical results are compared with the available experimental data.
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