ABINITIO CALCULATIONS OF THE C-13 MAGNETIC HYPERFINE PARAMETERS IN C-2+ USING NUMERICAL AND GAUSSIAN-BASIS SET METHODS

Ab initio calculations of the C-13 hyperfine coupling constants in C2+ (4-SIGMA-g-) were performed with extended Gaussian basis sets and the fully numerical, partial-wave multiconfiguration self-consistent field method. The basis set and numerical approaches are shown to yield results in good agreement with each other, as well as with the recent cryogenic neon matrix measurements. Single excitations reduce A(iso) by more than 40% with respect to the Hartree-Fock value, while double and higher excitations are needed to bring about good agreement with experiment. The best CI wavefunction produced values of A(iso) = 91.4 MHz, A(dip) = 2.8 MHz compared with experimental values of A(iso) = 95 +/- 1 MHz and A(dip) = 2 +/- 1 MHz.