Experimental evidence for long-lived HeAr2+ rare-gas dimers

The first observation of long-lived doubly charged HeAr2+ rare-gas dimers is reported. These dications were obtained in charge-stripping collisions of 850 keV HeAr+ in Ar gas. The mean lifetime for spontaneous dissociation of the 3He 40Ar2+ isotope was determined to be larger than about 40 μs using a new experimental technique. The cross-section for collision-induced dissociation of these molecular ions in air was found to be σdiss∼2×10−15 cm2. Calculations of the vibrational state population and mean lifetimes for a few low-lying electronic states indicate that all four low-lying states are very long lived and may be populated in fast charge-stripping collisions.