Knowledge Bank

Highly precise ground-state dipole moments of CaCl and CaBr were measured by using the molecular-beam laser-microwave double-resonance method. Microwave transitions were observed with linewidths of about 20 kHz. With an electric field applied Stark shifts of several hyperfine components were recorded. The determination of the dipole moment from measured line shifts required diagonalization of the complete energy matrix. Rotational constants were taken from M""{o}ller $etal.1$) and spin rotation and hfs constants from Childs $etal.2),3)$. The fit yielded the following results (statistical error in parentheses): [FIGURE] An additional systematic uncertainty of 0.02 D arises from the limited accuracy in determining the distance between the Stark plates but this does not affect the relative differences of the values. It will be shown that the Rittner ionic model fails in the calculation of these dipole moments. A modified model is proposed which takes into account explicitely the large charge shifts in the metal ions arising from the polarization.