Electric dipole moments of the cyclic trimers (H2O)(2)HCl and (H2O)(2)HBr from Stark effects in their rotational spectra

The electric dipole moments of two weakly bound cyclic trimers, (H2O)(2)HCl and (H2O)(2)HBr, have been determined from Stark effect measurements in ro tational spectra recorded at conditions of supersonic expansion. The experi mental results an compared with ab initio and induction calculations and th e dipole moments of all three monomers are found to be subject to appreciab le enhancement on complexation. The effect on the total dipole moment of ea ch trimer is, however, less marked owing to partial cancellation of the var ious component moments. A novel electrode system for Stark effect measureme nts in a cavity Fourier transform microwave spectrometer is also described. (C) 2000 Elsevier Science B.V. All rights reserved.