Microwave spectroscopy of mixed alkali halide dimers: LiNaF2

Abstract

Rotational spectra of 6LiNaF2 and 7LiNaF2 were measured by microwave absorption and Fourier-transform spectroscopy at different low rotational temperatures obtained by an adiabatic expansion in a beam and by collisional cooling in a cold absorption cell. Precise rotational constants, quartic centrifugal constants, quadrupole coupling constants, and the electric dipole moment were determined from least-squares fits of the experimental transition frequencies. Bond lengths and angles and the dipole moment are found to be in good agreement with recent ab initio calculations. As in homogeneous dimers, monomer to dimer 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.