Magnetically tunable Feshbach resonances in ultracold Li-Yb mixtures.

We investigate the possibility of forming Li+Yb ultracold molecules by magnetoassociation in mixtures of ultracold atoms. We find that magnetically tunable Feshbach resonances exist, but are extremely narrow for even-mass ytterbium isotopes, which all have zero spin. For odd-mass Yb isotopes, however, there is a new mechanism due to hyperfine coupling between the electron spin and the Yb nuclear magnetic moment. This mechanism produces Feshbach resonances for fermionic Yb isotopes that can be more than 2 orders of magnitude larger than for the bosonic counterparts.

Simultaneous bridge-localized and mixed-valence character in diruthenium radical cations featuring diethynylaromatic bridging ligands.

A series of bimetallic ruthenium complexes [{Ru(dppe)Cp*}(2)(µ-C≡CArC≡C)] featuring diethynylaromatic bridging ligands (Ar = 1,4-phenylene, 1,4-naphthylene, 9,10-anthrylene) have been prepared and some representative molecular structures determined. A combination of UV-vis-NIR and IR spectroelectrochemical methods and density functional theory (DFT) have been used to demonstrate that one-electron oxidation of compounds [{Ru(dppe)Cp*}(2)(µ-C≡CArC≡C)](HC≡CArC≡CH = 1,4-diethynylbenzene; 1,4-diethynyl-2,5-dimethoxybenzene; 1,4-diethynylnaphthalene; 9,10-diethynylanthracene) yields solutions containing radical cations that exhibit characteristics of both oxidation of the diethynylaromatic portion of the bridge, and a mixed-valence state. The simultaneous population of bridge-oxidized and mixed-valence states is likely related to a number of factors, including orientation of the plane of the aromatic portion of the bridging ligand with respect to the metal d-orbitals of appropriate π-symmetry.

Geometric phase for collinear conical intersections. I. Geometric phase angle and vector potentials.

We present a method for properly treating collinear conical intersections in triatomic systems. The general vector potential (gauge theory) approach for including the geometric phase effects associated with collinear conical intersections in hyperspherical coordinates is presented. The current study develops an introductory method in the treatment of collinear conical intersections by using the phase angle method. The geometric phase angle, η, in terms of purely internal coordinates is derived using the example of a spin-aligned quartet lithium triatomic system. A numerical fit and thus an analytical form for the associated vector potentials are explicitly derived for this triatomic A(3) system. The application of this methodology to AB(2) and ABC systems is also discussed.

Potential energy surfaces for the 1 (4)A('), 2 (4)A(') 1 (4)A(") and 2 (4)A(") states of Li(3).

Global potential energy surfaces for the 1 (4)A('), 2 (4)A('), 1 (4)A("), and 2 (4)A(") spin-aligned states of Li(3) are constructed as sums of a diatomics-in-molecules (DIM) term plus a three-body term. The DIM model, using a large basis set of 15 (4)A(") and 22 (4)A(') states, is used to obtain a "mixed-pairwise additive" contribution to the potential. A global fit of the three-body terms conserves the accuracy of the ab initio points of a full configuration-interaction calculation. The resulting fit accurately describes conical intersections for both the 1 (4)A(') and 2 (4)A(') surfaces with a root-mean-square (rms) deviation of 5.4x10(-5) hartree in D(infinityh) geometries and 1.2x10(-4) hartree in C(infinityv) geometries. The global fit appears to be quantitatively correct with a rms deviation of 1.8x10(-4)hartree for 1 (4)A('), 9.2x10(-4) hartree for 2 (4)A('), 2.5x10(-4) hartree for 1 (4)A("), and 5.1x10(-4) hartree for 2 (4)A("). A possible diabolic conical intersection, also called an accidental degeneracy, in C(2v) geometries, indicating a seam of conical intersections in C(s) geometries, is also found in ab initio calculations for A(2) states. As shown in this example, the DIM procedure can be optimized to describe the geometric phase and nonadiabatic effects in multisurface potentials.

New method for calculating bound states: the A(1) states of Li(3) on the spin-aligned Li(3)(1 (4)A(')) potential energy surface.

In this paper, we present a calculation for the bound states of A(1) symmetry on the spin-aligned Li(3)(1 (4)A(')) potential energy surface. We apply a mixture of discrete variable representation and distributed approximating functional methods to discretize the Hamiltonian. We also introduce a new method that significantly reduces the computational effort needed to determine the lowest eigenvalues and eigenvectors (bound state energies and wave functions of the full Hamiltonian). In our study, we have found the lowest 150 energy bound states converged to less than 0.005% error, and most of the excited energy bound states converged to less than 2.0% error. Furthermore, we have estimated the total number of the A(1) bound states of Li(3) on the spin-aligned Li(3)(1 (4)A(')) potential surface to be 601.

General laser interaction theory in atom-diatom systems for both adiabatic and nonadiabatic cases.

This paper develops the general theory for laser fields interacting with bimolecular systems. In this study, we choose to use the multipolar gauge on the basis of gauge invariance. We consider both the adiabatic and nonadiabatic cases and find they produce similar interaction pictures. As an application of this theory, we present the study of rovibrational energy transfer in Ar + CO collisions in the presence of an intense laser field.

Conical intersection between the lowest spin-aligned Li3(4A') potential-energy surfaces.

We have calculated new potential-energy surfaces for the lowest two spin-aligned (4)A(') states of the Li(3) trimer. This calculation shows a seam of conical intersections between these states resulting from the extra symmetry of the system when the atoms are in a collinear arrangement. This seam is especially important because of its proximity to the three-body dissociation limit of the system; ultracold scattering calculations and the bound-state energies of the system will be affected by the presence of this conical intersection. In this paper we discuss the calculation of the potential-energy surface and the location of the conical intersection seam.