Rotational Spectra of the Less Common Isotopomers, Electric Dipole Moment and the Double Minimum Inversion Potential of H2O···HCl

Abstract

Rotational spectra of 14 different isotopomers of the hydrogen-bonded dimer H2O···HCl have been measured. On application of a method of analysis designed to minimize the effect of vibration−rotation contributions to the ground state geometry, it was found that the experimental rotational constants imply a nonplanar geometry with R0(OCl) = 3.2273(3) A, and an out-of-plane bend angle of the water subunit φ0 = 34.7(4)°. This angle is consistent with results of ab initio calculations which, at the BSSE corrected, aug-cc-pVDZ/MP2 level, give φ = 46° for the equilibrium configuration and φ = 35.2° for the ground state. The electric dipole moment of H2O···HCl, μ = 3.437(4) D, was determined from Stark effect measurements and, after allowance for the zero-point inversion motion of the water subunit, leads to dipole moment enhancement on complexation Δμ = 0.81 D. Theoretical analysis of contributions to the chlorine nuclear quadrupole splitting constant χaa for H2O···HCl shows that most of the reduction relative t...