We present results of absorption measurements in dense cesium, rubidium and potassium vapor generated in all saphire cells (1,2). New spectral features or satellite bands in the neighbourhood of the second member of the cesium, rubidium and potassium principle series were found. We established no temperature dependence of  two peculiar diffuse features in the blue wing of the stronger component (np3/2, n=5,6,7 for potassium, rubidium and cesium, respectively)). By applying recent ab initio potential curves at large distances, we were able to construct corresponding difference potential curves with extrema responsible for the observed satellite bands. It appears that these extrema stem from the system of two close lying avoided crossings between ion-pair potential curve and long-range van der Waals potential curves emerging from several neighbouring atomic asymptotes (which also include second excited doublet of the p levels). The uppermost difference potential curve has one minimum and one maximum at very large interatomic distances, which in effect realizes bound electronic state of pure ion-pair character. The implications and aspects of such potentials for the case of ultracold K₂, Rb₂ and Cs₂ molecules will be discussed.

1. T. Ban, H. Skenderovic, R. Beuc and G. Pichler, Europhys.Lett. 48 (1999) 378.
2. T. Ban, S. Ter-Avetisyan, R. Beuc, H. Skenderovic and G. Pichler, Chem.Phys.Lett. 313 (1999) 110.