Theoretical study of low-lying electronic slates and emission spectra of the excimer ions NaHe+ and NaNe+

Ab initio CASSCF calculations using the Gaussian basis set aug_cc_pVTZ deve loped by Dunning et al. specifically for calculations at the post-HF level was carried out for excimer NaHe+ and NaNe+ ions in order to determine spec troscopic characteristics and radiation lifetimes of their low-lying excite d electronic states. The computed emission spectra of these were shown to b e in good agreement with the experimental ones observed recently by Hammer et al. (Hyperfine Interactions 88 (1994) 151). Contrary to the earlier popu lar opinion, all excited electronic states of these ions, correlating with the limit Rg(+) + Na, and not just the radiating singlet states turn out to be bound. It was shown that under the conditions of an experiment similar to the one performed by Hammer et al., the excited triplet NaHe+(1(3)Sigma( +)) states can decay as a result of their interactions with a high-energy A r+ beam. This decay has to be accompanied with the formation of the ions He +, which in turn can interact with sodium atoms to yield the radiating NaHe +(2(1)Sigma(+)) states again and, thus to maintain the emission observed in the experiment. (C) 1999 Elsevier Science B.V. All rights reserved.