Ab initiostudy of the electron-spin magnetic moments (g-factors) of C2−, CSi−, Si2−, LiC2, NaC2, and LiSi2

The electron-spin g-shifts of the title radicals are calculated using second-order perturbation theory, a Breit–Pauli Hamiltonian, and multireference configuration interaction (MRCI) wave functions. The isotropic 〈Δg〉 values (Δg=g−ge) are −830 for C2−(X2Σg+),−6515 for CSi−(X2Σ+), and −7595 for Si2−(12Σg+), in ppm, with ppm=10−6. For the X1A1 ground states of LiC2, NaC2, and LiSi2, they are −315, −290, and −7770 ppm, respectively. Experimental 〈Δg〉 values in Ar matrices, 3900 ppm for LiC2 and 3535 ppm for NaC2, do not agree with calculated results. However, those predicted for the π-type 12B1 excited state of LiC2 and NaC2 (3415 and 3635 ppm, with large parallel components of 9185 ppm for LiC2, and 10 350 ppm for NaC2) are in good agreement with the measured data. Thus, it appears that LiC2 and NaC2 were experimentally prepared, and their ESR spectra measured, in their lowest excited state 12B1. For the 12B1 state of LiSi2, 〈Δg〉 is about 9820 ppm. The latter value is mainly determined by a large g∥-shift of about 28 000 ppm.