High-level coupled-cluster methods for electron spin resonance spectra: on the experimental spectrum of the silacyclobutane radical cation

The silacyclobutane radical cation is a prototype intermediate in chemical reactions involving Si based organic molecules. In the interest of its full characterization, the experimentally determined isotropic hyperfine coupling constants of the hydrogens in silacyclobutane radical cation (c-SiC(3)(+)) have raised some interesting questions, leading to different interpretations of the spectrum. To help resolve this discrepancy, we report very high-level theoretical results with coupled-cluster theory using its analytical, response density matrix procedure, and recently proposed basis sets that are specific to ESR. The detailed studies of geometries, basis set effects, and electron correlation tend to support the B3LYP/6-31G-based reassignment of the ESR spectrum of the c-SiC(3)(+) radical cation by F?ngstr?m et al.