Theoretical study of the [ClHCl] pre-reactive complex

The van der Waals complex between the Cl(2P) atom and the HCl molecule was carefully investigated. Using high-level ab initio molecular orbital theory with extended basis sets, we analyse the effects of level of calculation, spin projection, basis set superposition error (BSSE), spin–orbit coupling, and harmonic zero-point energy (ZPE) on the energy changes. The non-collinear approach (12A′ ground state) shows a deeper well at 0 K, 401 cm−1, than the collinear approach (2Π ground state), 329 cm−1. It is concluded that these results represent the balance of a complicated interplay of many factors, which are affected by uncertainties in the theoretical calculations.