The in-plane force field of nitryl fluoride

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Abstract
The in-plane harmonic and some cubic force constants of nitryl fluoride (NO2F) have been determined from ab initio Hartree-Fock calculations, using 7s3p and 5s2p gaussian basis sets. The theoretical values are used to resolve the ambiguity of the experimental force constants. It is shown that of the two experimentally equivalent force fields of Mirri et al., Set I is the physically correct solution. However, as even Set I reproduces the isotope shift data poorly, a new experimental force field has been determined. The new force field agrees very well with the ab initio results and is considered the most reliable at present. It is stressed that isotope shifts are more effective in fixing the force field than centrifugal distortion constants ; the latter, although experimentally accurate, are significantly influenced by anharmonicity.