High-resolution laser spectroscopy of the A ← X transition of LiAr

Electronic structure and spectra of the RbAr van der Waals system including spin-orbit interaction

The potential energy curves and spectroscopic constants of the ground and excited states of the RbAr van der Waals system have been determined using a one-electron pseudopotential approach. This technique is used to replace the effect of the Rb(+) core and the electron-Ar interactions by effective potentials. The core-core interaction for Rb(+)Ar was incorporated using the accurate CCSD(T) potential of Hickling et al. [Hickling, H. L.; Viehland, L. A.; Shepherd, D. T.; Soldán, P.; Lee, E. P. F.; Wright, T. G. Phys. Chem. Chem. Phys. 2004, 6, 4233-4239]. This model reduces the number of active electrons of the RbAr van der Waals systems to just the single valence electron, permitting the use of very large basis sets for the Rb and Ar atoms. Using this approach, the potential energy curves of the ground and excited states dissociating into Rb(5s, 5p, 4d, 6s, 6p, 6d, and 7s) + Ar are calculated at the SCF level. Spin-orbit interaction was also considered within a semiempirical scheme for the states dissociating into Rb(5p) and Rb(6p). Spectroscopic constants are derived and compared with the available theoretical and experimental data. Such comparisons for RbAr show very good agreement for the ground and the first excited states. Furthermore, we have predicted the B(2)Σ(+)(1/2) ← X(2)Σ(+), A(2)Π(1/2) ← X(2)Σ(+), A(2)Π(3/2) ← X(2)Σ(+), A(2)Π(3/2) ← X(2)Σ(+), 5(2)Σ(+) ← X(2)Σ(+), 3(2)Π(1/2) ← X(2)Σ(+), and 3(2)Π(3/2) ← X(2)Σ(+) absorption spectra.

One-electron pseudopotential investigation of CsAr van der Waals system including the spin-orbit interaction

The potential energy curves of the ground state and many excited states of the CsAr van der Waals system have been determined using [Cs(+)] and [Ar] core pseudopotentials and by considering core polarization operators on both atoms. This has permitted to reduce the number of active electrons of the CsAr system to only one electron, i.e., the valence electron, which led to use of large basis sets for Cs and Ar atoms. In this context, the potential energy curves of the ground state and many excited states are performed at the self consistent field (SCF) level. Spin-orbit interaction is also considered within a semiempirical scheme for the states dissociating into Cs(6p) and Cs(5d). The core-core interactions for Cs(+)Ar is included using the coupled cluster simple and double excitation (CCSD) accurate potential of Hickling et al. (Hickling, H.; Viehland, L.; Shepherd, D.; Soldan, P.; Lee, E.; Wright, T. Phys. Chem. Chem. Phys. 2004, 6, 4233). In addition, the spectroscopic constants of these states are derived and compared with the available theoretical and experimental works. Such comparison has shown a very good agreement for the ground and the first excited states. However, the spectroscopic data for the higher excited states are presented for the first time.

Direct deperturbation analysis of the AΠ2∼BΣ+2 complex of LiAr7,6 isotopomers

Direct deperturbation analysis of the highly accurate experimental rovibronic term values of the A (2)Pi approximately B (2)Sigma(+) complex of LiAr [R. Bruhl and D. Zimmermann, J. Chem. Phys. 114, 3035 (2001)] has been performed in the framework of inverted close-coupling approach implicitly adjusted to the unified treatment of the overall A approximately B coupling effect without reducing the rovibrational dimensionality. The nonlinear fitting procedure was supported by the ab initio calculations on the spin-orbit and angular coupling matrix elements between the lowest X (2)Sigma(+), A (2)Pi, and B (2)Sigma(+) states. The analytical grid mapping based on the reduced variable representation of the radial coordinate r was used to improve the efficiency of the solution of the close-coupling radial equations near the dissociation limit. The mutual A approximately X perturbation effect on the A (2)Pi term values and spin-rotation splitting of the ground state were evaluated for both (7,6)LiAr isotopomers. The resulting empirical potential-energy curves for the adiabatic A (2)Pi and B (2)Sigma(+) states, along with the refined r-dependent nonadiabatic matrix elements, reproduce the total rovibronic structure of the (7)LiAr complex with the standard deviation of 0.003 cm(-1). The mass invariance of the deperturbed electronic parameters was confirmed by the calculation of the rovibronic term values of the (6)LiAr isotopomer which coincided with their experimental counterparts within 0.004 cm(-1).

Parallel temperatures in supersonic beams: ultracooling of light atoms seeded in a heavier carrier gas

Supersonic expansion is a very powerful tool to produce an atomic beam with a well defined velocity and, by seeding a test gas in such an expansion, the energy of the test gas can be transferred, at least partially, to the very-low-temperature carrier gas. The case usually studied is the one of a heavy gas seeded in a light carrier gas and, in this case, the parallel temperature of the seeded gas is always larger than the one of the carrier gas. In the present paper, we study the opposite case which has received less attention: when a light gas is seeded in a heavier carrier gas, the parallel temperature can be substantially lower for the seeded gas than for the carrier gas. This effect has been first observed by Campargue and co-workers in 2000, in the case of atomic oxygen seeded in argon. In the present paper, we develop a theoretical analysis of this effect, in the high dilution limit, and we compare our theoretical results to several experimental observations, including a set of measurements we have made on a beam of lithium seeded in argon. The agreement between theory and experiments is good.

Laser-Spectroscopic Investigation of Higher Excited Electronic States of the KAr Molecule

Higher excited electronic states of the van der Waals molecule 39KAr have been investigated using a supersonic beam and a two-step excitation. Four hundred seventy Doppler-free lines have been observed in the second step leading to the electronic states 5d2Sigma, 5d2Pi, 5d2Delta, and 7s2Sigma. The spectroscopic parameters of rotation, of spin-orbit splitting, of spin-rotation coupling, and of lambda-type doubling have been determined for altogether 19 vibrational levels of these electronic states. The molecular spin-orbit splitting turns out to be -0.42 cm-1 for 5d2Delta and -0.15 cm-1 for 5d2Pi, which is in fair agreement with the theoretical prediction for a Hund's coupling case a. The vibrational numbering was deduced from theoretical calculations of the interatomic potential. Six vibrational levels have been assigned to the 5d2Delta and the 5d2Sigma state, respectively, allowing a determination of the Dunham coefficients in these two states. For the equilibrium parameters of the 5d2Delta state, we obtain Re = 3.22(15) Å, De = 900(80) cm-1. Copyright 1999 Academic Press.