Electronic, vibrational and environmental effects on the hyperfine coupling constants of nitroside radicals. H2NO as a case study

The effect of polar solvents on the structure and EPR parameters of dihydronitrosyl radical H2NO have been investigated by a hybrid density functional/Hartree-Fock approach coupled to a proper description of vibrational averaging effects from the out of plane vibration and different polarizable continuum models for the description of the solvent. The adequacy of the electronic computations and averaging procedure are confirmed by the reliable results obtained for the isolated molecule. The shift in hyperfine couplings induced by the solvent is quantitatively reproduced, although the standard Onsager model saturates too quickly as a function of the dielectric constant. Introduction of the Block-Walker model rectifies matters and provides satisfactory results for polar solvents without hydrogen bonding capacity.