MICROWAVE SPECTROSCOPY OF MIXED-ALKALI HALIDE DIMERS - LINAF2

Rotational spectra of (LiNaF2)-Li-6 and (LiNaF2)-Li-7 were measured by microwave absorption and Fourier-transform spectroscopy at different low rotational temperatures obtained by and adiabatic expansion in a b eam and by collisional cooling in a cold absorption cell. Precise rota tional constants, quartic centrifugal constants, quadrupole coupling c onstants, and the electric dipole moment were determined from least-sq uares fits of the experimental transition frequencies. Bond lengths an d angles and the dipole moment are found to be in good agreement with recent ab initio calculations. As in homogeneous dimers, monomer to di mer bond expansions calculated from an ionic model are too large. The electric dipole moment from the ionic model is in excellent agreement with the ab initio result when experimental bond distances and angles are used and a 100% ionic character of the dimer bonds is assumed. (C) 1996 American Institute of Physics.