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.

Updated potential energy function of the Rb2 a(3)Σu(+) state in the attractive and repulsive regions determined from its joint analysis with the 2(3)Π0g state.

We report new experimental data for the Rb2 a(3)Σu(+) and 2(3)Π0g states obtained using the Perturbation Facilitated Infrared-Infrared Double Resonance (PFIIDR) technique. The results include ro-vibrational term values of the 2(3)Π0g state and resolved fluorescence spectra of the 2(3)Π0g→a(3)Σu(+) transitions for a wide range of rotational and vibrational quantum numbers. An analysis of these data confirms the initial assignment of the transitions to the a(3)Σu(+) state reported in our earlier work [B. Beser, V. B. Sovkov, J. Bai, E. H. Ahmed, C. C. Tsai, F. Xie, L. Li, V. S. Ivanov, and A. M. Lyyra, J. Chem. Phys. 131, 094505 (2009)]. The potential energy functions of the Rb2 a(3)Σu(+) and 2(3)Π0g states are derived from a simultaneous fit of the available experimental data. The improved potential function of the Rb2 a(3)Σu(+) state spans both the attractive and repulsive regions starting with internuclear distance R ∼ 4.5 Å.

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

Sets of experimental data on the Cs(2) a(3)Σ(u)(+) and 1(g) (3(3)Π(1g)) states, including the bound-bound and bound-free fluorescence spectra, are analyzed simultaneously to produce the potential energy curves of both states in the form of the Morse long range multiparameter function. The attractive branch of the a(3)Σ(u)(+) state potential is improved relative to the one reported in our earlier work [F. Xie, V. B. Sovkov, A. M. Lyyra, D. Li, S. Ingram, J. Bai, V. S. Ivanov, S. Magnier, and L. Li, J. Chem. Phys. 130, 051102 (2009)], in which the data on this state alone were analyzed. Besides, the new potential of this state also includes the repulsive branch in the range spanned by the bound-free fluorescence spectra. We have not found experimental evidence of the double minimum character of the 3(3)Π(1g) state potential, predicted by ab initio calculations, at least up to v = 8. This fact testifies that the upper state observed is better described by the Hund coupling case (c), in which the case (a) electronic basis states are intermixed by the strong spin-orbit interaction.

Experimental investigation of the 85Rb2 a 3Sigma(u)+ triplet ground state: multiparameter Morse long range potential analysis.

Using perturbation facilitated infrared-infrared double resonance excitation of the (85)Rb(2) molecule, we have observed spectrally resolved fluorescence to the a (3)Sigma(u)(+) state. We have analyzed the rovibrational energy level structure of the (85)Rb(2) a (3)Sigma(u)(+) state and derived a multiparameter Morse Long Range (MLR) potential and molecular constants for this state, which can be used to predict term values without needing to solve the radial Schrödinger equation.

Experimental investigation of the Cs2 a 3Sigma(u)+ triplet ground state: multiparameter Morse long range potential analysis and molecular constants.

We have observed the vibrational levels v(") = 0-40 of the Cs(2) a (3)Sigma(u)(+) state by perturbation facilitated infrared-infrared double resonance excitation and spectrally resolved fluorescence measurements, and derived a multiparameter Morse long range potential and molecular constants based on these data.

The K2 2(3)Pi(g) state: new observations and analysis.

Totally 3045 transitions into the 2(3)Pi(g) v = 0-42, J = 0-103, Omega = 0, 1, 2 rovibrational levels have been observed by infrared-infrared double resonance fluorescence excitation and two-photon spectroscopy. Molecular constants including the spin-orbit interaction parameters are obtained. Although the K2 2(3)Pi(g) state dissociates to the 4s + 3d atomic limit, it is strongly mixed with the 3P ionic states in the range of the potential well. This mixing results in a relatively large equilibrium internuclear distance Re = 5.254 A and a larger spin-orbit constant A0 approximately 14.17 cm(-1) than that of the atomic limit -2.33 cm(-1). Strong perturbations of the 2(3)Pi(g) levels observed are attributed to the spin-orbit coupling with the 4(1)Sigma(g)+ state.

Experimental study of the 39K2 2 3Pi(g) state by perturbation facilitated infrared-infrared double resonance and two-photon excitation spectroscopy.

The 39K2 2 3Pi(g) state has been observed by perturbation facilitated infrared-infrared double resonance and two-photon excitations. The vibrational numbering of the 2 3Pi(g) levels was determined by resolved fluorescence into the bound levels as well as to the continuum of the a 3Sigma(u)+ state. The rotational assignment of the 2 3Pi(g) levels excited by two-photon transitions was determined from excitation frequencies and resolved fluorescence into the bound levels of the a 3Sigma(u) + and b 3Pi(u) states. Molecular constants obtained from these observed levels agree with theoretical constants.