The rotational spectrum of the NF2 free radical: Determination of molecular structure

Many rotational transitions of nitrogen difluoride, NF2, have been recorded in the millimetre-wave region. By fitting the present and previous data together, it has been possible to determine several higher order centrifugal distortion terms and so refine the rotational and spin-rotational parameters. In addition, it has been possible to determine the off-diagonal electron spin-nuclear spin coupling parameter Tab for the two equivalent 19F nuclei. This term causes ortho-para mixing and, to our knowledge, this is the first time that such a term has been determined directly by spectroscopic means for spin 1/2 nuclei. Density- and wave-functional calculations employing moderately large to large basis sets have been carried out to test the reliability of such calculations and to corroborate the experimental hyperfine structural findings. In addition, vibration-rotation interaction terms were calculated theoretically in order to derive a mixed experimental/ab initio equilibrium structure for NF2 in the X2B1 state, namely:r=134.691(68)pmand∠=103.132(20)°.