Mean-lifetime calculations of the metastable doubly charged NeAr2+ rare-gas dimer.

Abstract

The energies and mean lifetimes of the different vibrational states of the $^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ electronic ground state of ${\mathrm{NeAr}}^{2+}$ have been calculated using the phase-shift technique. An efficient searching method for these narrow resonances was developed. The calculated lifetime of the v=12 vibrational state is in reasonable agreement with the experimental value of 275\ifmmode\pm\else\textpm\fi{}25 nsec, reported recently by Ben-Itzhak, Gertner, and Rosner [Phys. Rev. A 47, 289 (1993)], while the lifetimes of other states are more than three orders of magnitude off, thus determining the long-lived vibrational state detected unambiguously. From the difference between the calculated and measured mean lifetime, we have estimated that the potential curve of this 26-electron system is accurate to a few meV. We have also performed ab initio calculations of the $^{2}\mathrm{\ensuremath{\Sigma}}^{+}$ electronic ground state of ${\mathrm{NeAr}}^{+}$ and calculated the Franck-Condon factors for the final vibrational-state distribution of the ${\mathrm{NeAr}}^{2+}$ molecular ion produced in the ${\mathrm{NeAr}}^{+}$ charge-stripping collisions in order to estimate that high vibrational states are indeed produced in the experiment. We have also examined the validity of the WKB method for calculating the lifetimes of highly excited vibrational states.