Structure and energetics of gaseous HZnCl

The HZnCl molecule has recently been observed both in the gas phase and in argon matrixes, and the complexity of its spectrum has created big discrepancies between experimental and theoretically predicted Zn-H bond distances. In an attempt to resolve the questionable H-ZnCl bond length issue, as well as to study its stability relative to bond breakage, we have investigated at a very high ab initio level its geometric and energetic parameters. At the coupled cluster level of theory [CCSD(T)] with the new correlation-consistent basis sets for Zn by Balabanov and Peterson, and with the inclusion of core/valence and one-electron Douglas-Kroll-Hess relativistic effects, the basis set extrapolated H-ZnCl and HZn-Cl bond lengths have been calculated to be 1.499 and 2.079 A, compared with the experimental estimates of 1.596-1.789 and 2.08346 A, respectively. With the same procedure, the experimentally unknown bond length of ground-state ZnCl has been found to be equal to 2.122 A. As in the free diatomics ZnCl and ZnH, the HZn-Cl bond is stronger than the H-ZnCl bond by about 30 kcal/mol.