Electron-spin g-factors of H2−. An ab initio study

In ESR studies of γ-irradiated solid pH2, a peak is observed having a large positive g-shift, which, according to Symons (Chem. Phys. Lett. 247 (1995) 607), may be attributable to H2− trapped in the H2 matrix. To test this hypothesis, theoretical Δg-values for the resonant 2Σu+(1σg21σu) state of isolated H2− as computed at the ROHF level are reported. The calculated g-shifts are small negative (Δg‖ −27 ppm, Δg⊥ = −23 ppm), remaining close to Δg-value of −35 ppm for the H(2S) atom. The findings do not support the assertion that Δg(H2−) could be as high as + 1000 ppm.