Spin–orbit effects for the diatomic molecules containing halogen elements studied with relativistic effective core potentials: HX, X2 (X=Cl, Br and I) and IZ (Z=F, Cl and Br) molecules

Abstract

Abstract Spin–orbit effects on the spectroscopic constants (bond lengths, dissociation energies and harmonic vibrational frequencies) for HX, X 2 (X = Cl, Br and I) and IZ (Z = F, Cl and Br) molecules have been studied using shape-consistent relativistic effective core potentials (RECPs) with effective one-electron spin–orbit operator at HF, MP2, CCSD and CCSD(T) levels. Basis sets of pVTZ quality have been derived for Cl, Br and I for the present work. The spectroscopic constants calculated by the two-component RECP method are in good agreement with those from all-electron Dirac–Coulomb calculations with the basis sets of the similar quality at all levels of theory considered, suggesting that RECP methods mimic all-electron Dirac–Coulomb methods calculations rather well for molecules. Spin–orbit effects elongate the bond lengths, while reduce the dissociation energies and harmonic vibrational frequencies. From the spin–orbit effects on the spectroscopic constants, especially on dissociation energies of IF, ICl, IBr and I 2 , it is confirmed that the magnitude of spin–orbit effects increases in the F