Hyperfine structure in HCS and related radicals: a theoretical study

The hyperfine structure of the HCS radical and the isovalent HCO, HSiS and HSiO radicals was studied using the B3LYP and MRSDCI methods. The B3LYP calculations predict an isotropic proton hyperfine coupling constant a(H) of 127.4–129.1 MHz for HCS, in excellent agreement with the experiment. The calculations confirm the experimental fact that the a(H) value of HCS is much smaller than the a(H) values of HCO, HSiS and HSiO, for which we present a simple explanation on the basis of the analysis of the spin densities on the heavy atoms.