Spectroscopic and Thermochemical Properties of ClO, BrO, IO, and Their Anions Using Spinor-Based Coupled Cluster

A fully relativistic, spinor-based coupled cluster composite methodology is used to determine the spectroscopic constants and dissociation energies of ClO, BrO, IO, and their anions, as well as the electron affinities (EAs). This approach utilized the 4-component Dirac-Coulomb-Hamiltonian and thus includes spin at the orbital level in all calculations. Contributions associated with basis set truncation errors, outer-core electron correlation, the Gaunt interaction, and QED were applied. Coupled cluster singles, doubles, and triples (CCSDT) and CCSDT with perturbative quadruples [CCSDT(Q)] calculations were carried out to assess the effects of electron correlation beyond CCSD with perturbative triples [CCSD(T)] using a spinor basis. Resulting <i>D</i>₀ and EA values agree to well within 1 kcal/mol of the accurate experimental values. A detailed comparison is made to earlier work using a similar strategy but where scalar relativistic coupled cluster was combined with an <i>a posteriori</i> spin-orbit contributions. The results from the two approaches were found to be remarkably similar.