The electron-spin magnetic moment (g-tensor) of H2CO+ according to MRCI calculations

The electron-spin magnetic moment (g-tensor) of H2CO+((XB2)-B-2) is calculated using second-order perturbation theory, a Breit-Pauli Hamiltonian, and multireference configuration interaction wavefunctions. The dependency of the Delta g(aa) values (Delta g(aa) = g(aa) - g(e)) on the R(CO) bond length and CH2-angle is investigated. Second-order contributions to Delta g(xx) and Delta g(zz) are dominated by the magnetic coupling with just one or two excited states (e.g. 1(2)A(1) for Delta g(xx), and 1,2(2)B(1) for Delta g(zz)). The Delta g(zz) value is extremely sensitive to R(CO). At equilibrium, the calculated Delta g(xx), Delta g(yy), and Delta g(zz) values are 5510, -50, and 1296 ppm, respectively. The corresponding experimental data for H2CO+ isolated in Ne matrices are 4600, -800 and 200 ppm, with uncertainities of up to +/-500 ppm. Assuming that the matrix effects lower all g-shifts by about 900 ppm, our results are considered to be in good agreement with the experimental values expected for gas-phase H2CO+. They are also internally more consistent than those obtained in previous theoretical studies. (C) 2000 Elsevier Science B.V. All rights reserved.