M. Aubert-Frécon

Theoretical study of the electronic structure of the LiRb and NaRb molecules

Abstract The potential energy has been calculated over a wide range of internuclear distances for the 28 lowest molecular states of LiRb and NaRb molecules, using an ab initio method based on non-empirical pseudopotentials, parametrized l-dependent polarization potentials and full valence configuration interaction calculations. Molecular spectroscopic constants have been derived for the bound states with a regular shape. A good description of the experimentally known ground state for NaRb is obtained. Tables providing extensive data of energy values versus internuclear distances are available at the following address http://lasim.univ-lyon1.fr/allouche/lirbnarb.htm.

Multipolar long‐range electrostatic, dispersion, and induction energy terms for the interactions between two identical alkali atoms Li, Na, K, Rb, and Cs in various electronic states

For the alkali dimers Li2, Na2, K2, Rb2, and Cs2 long‐range potential energy curves of the molecular states corresponding to the asymptotes ns+ns and ns+np have been investigated from standard perturbation method up to second order in the multipolar expansion approximation of the interaction energy. Two different cases have been considered: (i) neglecting spin‐orbit effects and then values of the long‐range expansion coefficients Cn, n=(3), 6, 8, (10) have been determined (ii) including spin‐orbit effects and then potential energy curves have been determined numerically and are graphically displayed. Very good agreement is obtained between present curves and very recent long‐range experimental ones for the X 1Σ+g state of Li2 and for the X 1Σg+ and 1Πg states of Na2. The position and the energy of purely long‐range extrema of the states 1u(2S1/2+ 2P1/2), 1u(2S1/2+2P3/2) and 0g−(2S1/2+2P3/2) have been determined for each alkali dimer investigated.

Theoretical electronic structure of RbCs revisited

The potential energy for the 30 lowest molecular states 2S + 1Λ( + ) of the RbCs molecule has been calculated over a wide range of internuclear distances, using an ab initio method based on non-empirical pseudopotentials, parametrized l-dependent polarization potentials and full valence CI calculations. Molecular spectroscopic constants have been derived for the bound states. An accurate description of the few experimentally known states is obtained. Extensive tables of energy values versus internuclear distances are available at the following address: http://lasim.univ-lyon1.fr/allouche/rbcs.htm.

Static dipole polarizability of small mixed sodium–lithium clusters

We have measured the static dipole polarizability of Nay−xLix clusters (with y=2, 3, 4, and 8) by molecular beam deflection technique. For a given size, the polarizability of pure lithium clusters is smaller than the polarizability of pure sodium clusters. For mixed clusters, a smooth decrease in the polarizability is observed as the proportion of lithium atoms increases. For the NaLi molecule, both experimental permanent dipole and average polarizability have been obtained. Experimental results are compared to results of density functional theory and configuration interaction single and double (CISD) ab initio calculations.

Calculated long‐range potential‐energy curves for the 23 molecular states of I2

The interaction energy is calculated for the 23 molecular states of I2 as a sum of the quadrupolar electrostatic and dispersion energy terms in the multipole expansion for values of the internuclear separation R larger than 7 A. For each state the potential energy curve and the multipolar expansion coefficients C5 and C6 are displayed. Results in fair agreement with experimental potential energy curves are obtained for the X O+g and the B O+u states. The relative importance of electrostatic and dispersion energy terms is quoted, as well as the attractive or repulsive feature of each state. The determination of the wave functions is also considered.

The theoretical spin-orbit structure of the RbCs molecule

The potential energy has been calculated for the 49 lowest molecular states Ω( + /-) of the molecule RbCs within the 5-23 a0 range of internuclear distances R. Spin-orbit interactions are taken into account through a semi-empirical spin-orbit pseudo-potential added to the electrostatic Hamiltonian. Molecular spectroscopic constants have been derived for bound states in the vicinity of their (inner) well. To the best of our knowledge, the vast majority of the results presented here are the first for this molecule. Extensive tables presenting energy values versus R are available at the following address: http://lasim.univ-lyon1.fr/allouche/rbcs-so.htm.

Long-range molecular states dissociating to the three or four lowest asymptotes for the ten heteronuclear diatomic alkali molecules

Abstract Long-range energy matrix elements have been calculated in the multipolar expansion approximation for all the molecular states dissociating to the three or four lowest asymptotes for the molecules LiNa, LiK, LiRb, LiCs, NaK, NaRb, NaCs, KRb, KCs and RbCs using the semi-empirical perturbative model we proposed recently. Two different assumptions have been investigated: including or excluding the spin-orbit effects within each atom. Full numerical results are presented for NaK and LiCs which have been chosen as examples. For the ten molecules in the non-interacting assumption the long-range coefficients C 6 and C 8 have been found for each state when neglecting atomic spin-orbit effects while the fitted value C * 6 and C * 8 are presented for each state when including atomic spin-orbit effects. When considering the interacting states, those dissociating to n s + n ′s and to n s + 5d(Cs) are seen to be slightly perturbed while the states dissociating to n s + n ′p and to n p + n ′s are significantly perturbed. The wavefunctions for the interacting 3 Σ + , 3 Π, 0 + , 0 − , 1, 2 states for the molecules NaK and LiCs are presented for various internuclear distances.

New approach for the electronic energies of the hydrogen molecular ion

Abstract Herein, we present analytical solutions for the electronic energy eigenvalues of the hydrogen molecular ion H 2 + , namely the one-electron two-fixed-center problem. These are given for the homonuclear case for the countable infinity of discrete states when the magnetic quantum number m is zero, i.e., for 2Σ+ states. In this case, these solutions are the roots of a set of two coupled three-term recurrence relations. The eigensolutions are obtained from an application of experimental mathematics using Computer Algebra as its principal tool and are vindicated by numerical and algebraic demonstrations. Finally, the mathematical nature of the eigenenergies is identified.

Theoretical determination of highly excited states of K2 correlated adiabatically above K(4p)+K(4p)

The electronic structure of the K(2) molecule is revisited to describe the 36 highly excited states dissociating into the three limits K(4s) + K(4f), K(4s) + K(6p), and K(4s) + K(5d), which have not yet been investigated theoretically. Potential energy curves and spectroscopic constants are (re)displayed for the 98(1,3)Lambda(g,u) ((+,-)) molecular states correlated adiabatically to the limits up to K(4s) + K(5d). For the 10 states dissociating adiabatically into K(4p) + K(4p) and limits above for which experimental data are available, averaged errors of present results are found to be Delta R(e) = 0.07a(0), Delta T(e) = 50 cm(-1), Delta omega(e) = 0.8 cm(-1) and Delta D(e) = 60 cm(-1). Full energy data are available at the following address http://lasim.univ-lyon1.fr/allouche/k2.html

A ligand-field approach for the low-lying states of Ca, Sr and Ba monohalides

Abstract The ligand field approach proposed by Rice, Martin and Field (J. Chem. Phys. 82 (1985) 5023) to describe the low-lying states of calcium monohalides has been extended to strontium and barium monohalides. Molecular wavefunctions are described in terms of model potential functions for alkaline earth ions. Transition energies, permanent and transition dipole moments have been evaluated. The three lowest excited states of each molecule are seen to be correctly represented in this way, the better agreement with experiment being displayed for barium compounds.