We report a computational study of the potential energy surface (PES) and vibrational bound states for the ground electronic state of Li2+Kr. The PES was calculated in Jacobi coordinates at the Restricted Coupled Cluster method RCCSD(T) level of calculation and using aug-cc-pVnZ (n = 4 and 5) basis sets. Afterward, this PES is extrapolated to the complete basis set (CBS) limit for correction. The obtained interaction energies were, then, interpolated numerically using the reproducing kernel Hilbert space polynomial (RKHS) approach to produce analytic expressions for the 2D-PES. The analytical PES is used to solve the nuclear Schrodinger equation to determine the bound states’ eigenvalues of Li2+Kr for a J = 0 total angular momentum configuration and to understand the effects of orientational anisotropy of the forces and the interplay between the repulsive and attractive interaction within the potential surface. In addition, the radial and angular distributions of some selected bound state levels, which lie below, around, and above the T-shaped 90° barrier well, are calculated and discussed. We note that the radial distributions clearly acquire a more complicated nodal structure and correspond to bending and stretching vibrational motions “mode” of the Kr atom along the radial coordinate, and the situation becomes very different at the highest bound states levels with energies higher than the T-shaped 90° barrier well. The shape of the distributions becomes even more complicated, with extended angular distributions and prominent differences between even and odd states.
Dissociative photoionization of the He···Li2 van der Waals complex to the ground electronic state of the He···Li2+ ion is investigated theoretically. The photoionization cross section is computed using existing interaction potentials. Resonances are found on top of a structured continuum. They are assigned to vibrational predissociation of the ion by comparison with Fermi Golden Rule calculations. Because of the differences in potential energy surfaces between the neutral and ionic complexes, only the resonances corresponding to quasibound states with the highest excitation in the van der Waals modes are visible. The other quasi bound states obtained in the Fermi Golden Rule calculations can give information on vibrational energy relaxation rates in other collisional processes involving the lithium dimer ion and a helium atom.
The geometric structures and the relative stability of the Li+−Nen clusters, with n = 1–20, have been computed using pairwise model potential and density functional theory (DFT) method. The potential energy surface employed in these calculations is based on the Li+-Ne, Ne-Ne and many body interactions V3B. A series of methods and basis sets have been tested by reproduce correctly the experimental Li+-Ne and Ne-Ne potential energies. In addition, both Li+-Ne and Ne-Ne numerical potentials have been fitted by several analytical expressions as Tang and Toennies (TT), Extended Lennard Jones (ELJ) and Lennard-Jones (LJ) formula. The most stable structures of Li+-Nen clusters up to n = 20 have been optimized at Basin Hopping Monte Carlo (BHMC) method. The accuracy of our pairwise potential model has been confirmed by re-optimization at the DFT level of theory. The relative stabilities of Li+-Nen clusters are discussed by calculating the energy per neon atom, the first derivative, the fragmentation energy and the second derivative as well as the Highest Occupied Molecular orbital (HOMO)–Lowest Unoccupied Molecular Orbital(LUMO) energy gap with the size of the clusters. It was shown that n=6, 8, 12, 14, 16 and 17 correspond to the magic numbers. Finally, thermodynamic properties are calculated and showed that the formation process of Li+-Nen clusters is endothermic and non-spontaneous.
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