Theoretical calculations for the ground state and for 83 excited states of the Na2 molecule are presented in the framework of two independent approaches. The electron–core interaction is represented either by a pseudopotential or by a model potential, and a core polarization potential is introduced in both cases. The basis set contains either Gaussian orbitals or two-center generalized Slater orbitals. The two methods appear to give similar results, one being more accurate for the ground and first excited states, the other being better adapted to the intermediate Rydberg states. A very good agreement is obtained with the experimental spectroscopic constants determined for 26 states, the mean deviation being ΔRe=0.05a0, Δωe=0.86 cm−1, and ΔDe=57 cm−1.
Potential curves of the K 2 and NaK molecules have been computed in the framework of pseudopotential methods, over a wide range of interatomic distances. At short internuclear distances, the agreement with experimental data is excellent, the mean deviation between theoretical and experimental spectroscopic constants being 1% for the two alkali dimers. At large interatomic separation, wells and avoided crossings are observed in adiabatic potential curves of highly excited states correlated to the asymptotes close to K[4p]ϩK[4p] and Na[3p]ϩK [4p]. For example, the well depths of the 1 ⌺ ϩ states reach 2650 cm Ϫ1 for K 2 and 4330 cm Ϫ1 in the case of NaK. We demonstrate that they correspond to pseudocrossings between covalent states ͑dissociating into K[nl]ϩK [nЈlЈ] or Na[nl]ϩK[nЈlЈ]͒ and ionic states ͑correlated to K ϩ ϩK Ϫ for K 2 , Na ϩ ϩK Ϫ , or Na Ϫ ϩK ϩ for NaK, the negative ion being in the ground state or an autoionizing state͒. As for Na 2 , these structures may play a crucial role in the interpretation of low-energy collisions. ͓S1050-2947͑96͒05905-8͔ PACS number͑s͒: 31.15.Ar; 31.50.ϩw; 33.20.Ϫt * Present address: Laboratoire de Spectrométrie Ionique et Moléculaire, CNRS URA No. 171, Bât. 205,
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