A theoretical study of the X2NO systems (X=F,Cl,Br,I): effects of halogen substitution on structural and spectroscopic properties

Structural and spectroscopic properties of the X2NO series of radicals, with X = F, Cl, Br, I, have been computed by the coupled cluster ansatz in conjunction with hierarchical series of basis sets, accounting for, in most cases, core correlation effects and extrapolation to the complete basis set limit. Namely, equilibrium structures, vibrational frequencies, and hyperfine coupling constants have been considered. Methods rooted into the density functional theory have been used to estimate anharmonic and, in conjunction with the polarizable continuum model, environmental effects. The remarkable agreement with the available experimental data, limited to the lighter member of the series, confirms the reliability of our computational approach and suggests that the data for heavier species represent reliable benchmarks for future experimental data and/or cheaper computational methods devised for larger systems.