An ab initio study of the magnetic hyperfine properties of F-2(2Σ+u)

Gaussian basis sets derived from the new Dunning ''correlation consistent'' sets have been used in conjunction with multireference single- and double-excitation configuration interaction (CI) wave functions to determine the magnetic hyperfine properties of the F-2 radical anion and the electron affinity of F2. The best computed values, using an extension to the polarized, valence quadruple zeta basis (cc-pVQZ) are: Aiso(19F)=772 MHz (expt=785 MHz), Adip=890 MHz (expt=901 MHz), and EA=2.61 eV (expt=3.08±0.10 eV). Estimates which crudely account for basis set incompleteness and CI truncation lead to the following, slightly different, values: Aiso (19F)=802 MHz, Adip =898 MHz, and EA=2.94 eV. The sensitivity of Aiso to changes in the F--F bond length results in an uncertainty on the order of ±20 MHz in the isotropic hyperfine property. Such close agreement between theory and experiment suggests that any rare gas matrix effect in the recent electron spin resonance (ESR) measurements on F-2 should be small, i.e., the matrix results should agree well with any future gas phase values. Correlation effects beyond the standard singles and doubles level are estimated to contribute approximately 50 MHz (∼30%) of the 155 MHz correlation correction to Aiso