The 4s and 5s Rydberg excited states of NaAr(n)* clusters are investigated using a pseudopotential quantum-classical method. While NaAr(n) clusters in their ground state are known to be weakly bound van der Waals complexes with Na lying at the surface of the argon cluster, isomers in 4s or 5s electronically excited states of small NaAr(n)* clusters (n< or =10) are found to be stable versus dissociation. The relationship between electronic excitation and cluster geometry is analyzed as a function of cluster size. For both 4s and 5s states, the stable exciplex isomers essentially appear as sodium-centered structures with similar topologies, converging towards those of the related NaAr(n)+ positive ions when the excitation level is increased. This is consistent with a Rydberg-type picture for the electronically excited cluster, described by a central sodium ion solvated by an argon shell, and an outer diffuse electron orbiting around this NaAr(n)+ cluster core.

No abstract

The adiabatic potential energy curves and the permanent and transition dipole moments of the low-lying electronic states of the NaLi molecule dissociating into Na(3s, 3p, 4s, 3d, 4p) + Li(2s, 2p, 3s, 3p, 3d) have been investigated. The molecular calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Na+ and Li+ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations through the CIPCI quantum chemistry package. The derived spectroscopic constants of the ground state and lower excited states are in good agreement with available experimental and theoretical works. However, the 7–101,3Σ+, 5–71Π, 2–63Π and 1–31,3Δ excited states are studied for the first time. The permanent dipole moment of NaLi has revealed both ionic characters relating to electron transfer and yielding Na+Li− and Na−Li+ arrangements. The transition dipole moment is used to evaluate the radiative lifetimes of the vibrational levels trapped in the 21Σ+ excited state for the first time. In addition to the bound–bound contribution, the bound-free term has been evaluated exactly using the Franck–Condon (FC) approximation and added to the total radiative lifetime.

No abstract

Experiments with cold ion–atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an alkali-metal atom: CaAlk+ (Alk = Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotentials, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potential energy curves, spectroscopic constants, and transition and permanent electric dipole moments are determined and analyzed for the ground and excited electronic states. We examine the prospects for ion-neutral reactive processes and the production of molecular ions via spontaneous radiative association and laser-induced photoassociation. After that, spontaneous and stimulated blackbody radiation transition rates are calculated and used to obtain radiative lifetimes of vibrational states of the ground and first-excited electronic states. The present results pave the way for the formation and spectroscopy of calcium–alkali-metal-atom molecular ions in modern experiments with cold ion–atom mixtures.

Ab initio many-electron study for the low-lying states of the alkali hydride cations in the adiabatic representation Theoretical calculation of the excited states of the KCs molecule including the spin-orbit interactionThe potential curves and spectroscopic constants of the excited states of alkali-argon diatomics MRg ͑MϭLi, Na and K, RgϭAr͒ are calculated using usual semilocal single valence electron pseudopotentials on alkali atoms ͓͑M ϩ ͔-core pseudopotentials͒, semilocal pseudopotentials replacing all the electrons of argon ͓͑Ar͔-core pseudopotentials͒, and core polarization pseudopotentials on both centers. All states dissociating into Li͑2s, 2p, 3s, 3p, 3d, 4s, and 4p͒, Na͑3s, 3p, 3d, 4s, 4p, 4d, 5p͒ and K͑4s, 4p, 5s, 3d, 5p, 4d, 6s, 4f , 6p, 5d, 7s, 5f ͒ are considered. The core-core interactions for Li ϩ Ar and Na ϩ Ar are included using the accurate ab initio potentials of Ahmadi et al. ͓G. R. Ahmadi, J. Almlöf, and I. Roeggen, Chem. Phys. 199, 33 ͑1995͒; G. R. Ahmadi and I. Roeggen, J. Phys. B 27, 5603 ͑1994͔͒ while the K ϩ Ar ion data are determined by MP2 all-electron calculations.

No abstract

No abstract