Joint analysis of the Cs2 a3Σu+ and 1g (3(3)Π1g) states

The Rb2 31Π g state: Observation and analysis

This paper reports observations and analysis of the Rb₂ 3¹Π _g state. A total of 323 rovibrational term values spanning the range of the rotational quantum number J = 7 through 77 and the vibrational quantum number v = 2 through 23 (about 1/3 of the potential well depth) were measured using the optical-optical double resonance technique. The term values are simulated within a model of a piece-wise multi-parameter potential energy function based on the generalized splines. This function not only enables a reproduction of the experimental data with a reasonable quality but also approximates the available ab initio function in its whole range with a uniform accuracy.

Re-examination of the Cs2 ground singlet X1Σg+ and triplet a3Σu+ states

This paper clarifies the disagreement in the depth of the potential energy curve of the cesium dimer singlet ground state which has lasted for nearly a decade. We point out that the origin of this disagreement must be a technical misprint in the values of the three binding energies reported by Danzl et al. [Science 321, 1062 (2008)], while the X¹Σ_g⁺ state potential reported by Coxon and Hajigeorgiou [J. Chem. Phys. 132, 094105 (2010)], based on experimental data by Amiot and Dulieu [J. Chem. Phys. 117, 5155 (2002)], is quite correct. We have recalculated the potential energy function of the triplet ground state a³Σ_u⁺ by using the available experimental data spanning both the attractive and the repulsive branches so that the potential energy function complies asymptotically with the singlet ground state X¹Σ_g⁺ potential energy function by Coxon and Hajigeorgiou. This is important for the simulation of the near dissociation properties such as Feshbach resonances, which are typically observed in modern experiments with ultracold atoms and molecules.

An accurate potential model for the a3Σu+ state of the alkali dimers Na2, K2, Rb2, and Cs2

A modified semi-empirical Tang-Toennies potential model is used to describe the a³Σ_u⁺ potentials of the alkali dimers. These potentials are currently of interest in connection with the laser manipulation of the ultracold alkali gases. The fully analytical model is based on three experimental parameters, the well depth D_e, well location R_e, and the harmonic vibrational frequency ω_e of which the latter is only slightly optimized within the range of the literature values. Comparison with the latest spectroscopic data shows good agreement for Na₂, K₂, Rb₂, and Cs₂, comparable to that found with published potential models with up to 55 parameters. The differences between the reduced potential of Li₂ and the conformal reduced potentials of the heavier dimers are analyzed together with why the model describes Li₂ less accurately. The new model potential provides a test of the principle of corresponding states and an excellent first order approximation for further optimization to improve the fits to the spectroscopic data and describe the scattering lengths and Feshbach resonances at ultra-low temperatures.

Observations and analysis with the spline-based Rydberg-Klein-Rees approach for the 3(1)Σg(+) state of Rb2

Ro-vibrational term values of the 3(1)Σg (+) state of (85,85)Rb2 and (85,87)Rb2 and resolved fluorescence spectra to the A(1)Σu (+) state are recorded following optical-optical double resonance excitation. The experimental data are heavily perturbed, and as a result, the standard analysis based on Dunham series representation of the energy levels fails. The analysis is done via modeling the adiabatic potential function with the Rydberg-Klein-Rees potential constructed from the generalized smoothing spline interpolation of the vibrational energies Gv and rotational constants Bv.

Observation and deperturbation of near-dissociation ro-vibrational structure of the Cs2 state 0u(+) (A(1)Σu(+)∼b(3)Π0+u) at the asymptote 6S1/2 + 6P1/2

New ro-vibrational structures of cold Cs2 in the 0u(+) state near the asymptote 6S1/2 + 6P1/2 are resolved. The variation of the rotational constants shows that the related energy spectra are strongly perturbed. An analysis of new data along with the empirical and theoretical information available from other sources is performed. For this purpose the model of spin-orbit coupling of the Hund's case (a) states A(1)Σu(+)∼b(3)Πu proposed by Bai et al. [Phys. Rev. A 83, 032514 (2011)] is extrapolated to the dissociation limit, and the parameters of the extrapolation are fitted from the near-dissociation experimental data.

Binding energies of the ground triplet state a(3) Σ(u)(+) of Rb2 and Cs2 in terms of the generalized Le Roy-Bernstein near-dissociation expansion

Formulae of Le Roy-Bernstein near-dissociation theory are derived in a general isotope-invariant form, applicable to any term in the rotational expansion of a diatomic ro-vibrational term value. It is proposed to use the generalized Le Roy-Bernstein expansion to describe the binding energies (ro-vibrational term values) of the ground triplet state a(3) Σ(u)(+) of alkali metal dimers. The parameters of this description are determined for Rb2 and Cs2 molecules. This approach gives a recipe to calculate the whole variety of the binding energies with characteristic accuracies from ∼1 × 10(-3) to 1 × 10(-2) cm(-1) using a relatively simple algebraic equation.