Comparing electron-sping-tensor results of first-row radicals with those of higher rows

Abstract

The electron‐spin Δg values of radicals from the first and second row with 9–15 valence electrons (VE) were calculated using second‐order perturbation theory and a Breit–Pauli Hamiltonian, in conjunction with multireference configuration interaction (MRCI) wave functions. The radicals studied include CO+, SiO+, BO, AlO, BeF, MgF, and CaF, with 9 valence electrons; M+O −2 and M+S −2 (M = Li, Na), with 13 VEs; and F −2, Cl −2, and FCl−, with 15 VEs. Our method works well for first‐ and second‐row systems. Comparing with experimental results for 9 and 15 VE radicals trapped in rare‐gas matrices, Δg⊥ components (usually large) are described within 10%, whereas most calculated Δg‖ values (usually small) are much smaller than the experimental ones. The Δg⊥ values of the mixed first–second row systems SiO+ and AlO, due to a mutual cancellation of the contributions from the lowest two 2Π states, are relatively small (≈ −2500 ppm). Also, reliable g shifts for SiO+ and AlO can only be calculated using natural orbitals, as the molecular orbital treatment gives incorrect ground‐state spin‐density distributions. Difficulties previously found by a density functional theory/gauge including atomic orbitals (DFT/GIAO) study on the g shifts of AlO are thus most probably caused by the use of inacurrate spin densities rather than the possible failure of the perturbation expansion truncated at second order. For the π radicals MO2 and MS2, Δg‖ is very large due to the coupling of two close‐lying states having similar spin‐density distributions. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 324–335, 2000

The and states of N2+: hyperfine and nuclear quadrupole coupling constants, electric quadrupole moments, and electron-spin g-factors. A theoretical study

“…-data. As discussed elsewhere [59][60][61], 1 2 R þ ðgÞ radicals with 9 valence electrons are expected to have negative Dg ? Õs (g ?…”

Prediction of electron paramagnetic resonance g values using coupled perturbed Hartree–Fock and Kohn–Sham theory

“…The field was revived by Lushington and Grein 18 -21 who made important contributions to the ab initio prediction of g values at the Hartree-Fock ͑HF͒ and more, recently, also at the MR-CI level. 18,21 While the HF level methods can also be applied to larger molecules, the much more demanding MR-CI methodology is restricted to small molecules where, however, it gives accurate results. Since all of these ab initio approaches are formulated as sum-over-states ͑SOS͒ theories it is necessary to explicitly generate a sufficient number of excited state wave functions which is a laborious and time consuming task.…”

Efficient calculation of electron paramagnetic resonance g-tensors by multireference configuration interaction sum-over-state expansions, using the atomic mean-field spin–orbit method

“…Obviously, case ͑i͒ is ideal, and case ͑iii͒ is bad. The situation is especially difficult if the SOS consists of two similarly large terms of opposite sign, as in the case of AlO, 13,14 H 2 CO ϩ , 15 and other radicals.…”