The electric dipole moment of tetrahydropyran–water

Using Stark-effect Fourier-transform microwave spectroscopy, the electric dipole moment components of tetrahydropyran–H2O were measured to be |μa|=1.6034(3) D and |μc|=0.9881(11) D. The a- and c-type spectra of the complex were observed. No b-type spectrum was found, consistent with ab initio geometries, which have a plane of symmetry in this hetero-dimer. Supported by these findings the μb component of the dipole moment was fixed to zero. Adjusting the two remaining components, the Stark splittings can be reproduced within the experimental uncertainty. The ab initio dipole calculation, performed using the MP2/Spackman basis, shows that the measured dipole moment is only consistent with an axial–anti-configuration of the complex.