Collision-Induced Spin Exchange of Alkali-Metal Atoms With 3^3He: An Ab Initio Study

We present a rigorous quantum study of spin-exchange transitions in collisions of the alkali-metal atoms with $^3$He in the presence of an external magnetic field. Using accurate ab initio interaction potentials, we obtain refined estimates for the Fermi contact interaction constants for complexes of Na, K, and Rb atoms with $^3$He. Ab initio calculations show that the Fermi contact interaction in Li-$^3$He varies more slowly with inter-nuclear distance than predicted by the atomic model [R. M. Herman, Phys. Rev. 37, A1062 (1965)]. The calculated spin-exchange rate constants for Na, K, and Rb atoms in a gas of $^3$He are in good agreement with experimental data. Our calculations demonstrate that at a temperature of 0.5 K, collision-induced spin exchange of the alkali-metal atoms occurs at a very slow rate of ~10$^−22$ cm$^3$/s, suggesting potential applications in cryogenic cooling, precision spectroscopy, and quantum optics.Astronom

Suppression of Zeeman Relaxation in Cold Collisions of 2P1/2^2P_{1/2} Atoms

We present a combined experimental and theoretical study of angular momentum depolarization in cold collisions of $^2P$ atoms in the presence of an external magnetic field. We show that collision-induced Zeeman relaxation of Ga$^2P_{1/2}$ and In $^2P_{1/2}$ atoms in cold $^4$He gas is dramatically suppressed compared to atoms in $^2P_{3/2}$ states. Using rigorous quantum-scattering calculations based on ab initio interaction potentials, we demonstrate that Zeeman transitions in collisions of atoms in $^2P$ electronic states occur via couplings to the $^2P_{3/2}$ state induced by the anisotropy of the interaction potential. Our results suggest the feasibility of sympatheticthetic cooling and magnetic trapping of $^2P_{1/2}$-state atoms, such as halogens, thereby opening up exciting areas of research in precision spectroscopy and cold-controlled chemistry.Physic

Collision-Induced Spin Depolarization of Alkali-metal Atoms in Cold 3^3He Gas

We present a joint experimental and theoretical study of spin depolarization in collisions of alkali-metal atoms with $^3$He in a magnetic field. A rigorous quantum theory for spin-changing transitions is developed and applied to calculate the spin exchange and spin relaxation rates of Li and K atoms in cryogenic $^3$He gas. Magnetic trapping experiments provide upper bounds to the spin exchange rates for Li-$^3$He and K-$^3$He, which are in agreement with the present theory. Our calculations demonstrate that the alkali-metal atoms have extremely slow spin depolarization rates, suggesting a number of potential applications in precision spectroscopy and quantum optics.Physic

On the role of the magnetic dipolar interaction in cold and ultracold collisions: Numerical and analytical results for NH(3Σ−^3\Sigma^-) + NH(3Σ−^3\Sigma^-)

We present a detailed analysis of the role of the magnetic dipole-dipole interaction in cold and ultracold collisions. We focus on collisions between magnetically trapped NH molecules, but the theory is general for any two paramagnetic species for which the electronic spin and its space-fixed projection are (approximately) good quantum numbers. It is shown that dipolar spin relaxation is directly associated with magnetic-dipole induced avoided crossings that occur between different adiabatic potential curves. For a given collision energy and magnetic field strength, the cross-section contributions from different scattering channels depend strongly on whether or not the corresponding avoided crossings are energetically accessible. We find that the crossings become lower in energy as the magnetic field decreases, so that higher partial-wave scattering becomes increasingly important \textit{below} a certain magnetic field strength. In addition, we derive analytical cross-section expressions for dipolar spin relaxation based on the Born approximation and distorted-wave Born approximation. The validity regions of these analytical expressions are determined by comparison with the NH + NH cross sections obtained from full coupled-channel calculations. We find that the Born approximation is accurate over a wide range of energies and field strengths, but breaks down at high energies and high magnetic fields. The analytical distorted-wave Born approximation gives more accurate results in the case of s-wave scattering, but shows some significant discrepancies for the higher partial-wave channels. We thus conclude that the Born approximation gives generally more meaningful results than the distorted-wave Born approximation at the collision energies and fields considered in this work.Comment: Accepted by Eur. Phys. J. D for publication in Special Issue on Cold Quantum Matter - Achievements and Prospects (2011

Scattering of Stark-decelerated OH radicals with rare-gas atoms

We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH (X\,^2\Pi_{3/2}, J=3/2, f) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D$_2$ as a function of the collision energy between $\sim 70$ cm$^{-1}$ and 400~cm$^{-1}$. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on accurate \emph{ab initio} potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [Gilijamse \emph{et al.}, Science {\bf 313}, 1617 (2006)], Ar [Scharfenberg \emph{et al.}, Phys. Chem. Chem. Phys. {\bf 12}, 10660 (2010)], He, and D$_2$ [Kirste \emph{et al.}, Phys. Rev. A {\bf 82}, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.Comment: 10 pages, 5 figure

Cold Collisions of OH(2Π) Molecules with He Atoms in External Fields†

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The RgI2 (ion-pair states) van der Waals complexes

This paper is an overview of our recent experimental investigations of the RgI2 van der Waals complexes, Rg = He, Ar, Kr, performed by means of laser induced fluorescence spectroscopy, optical-optical double resonance and supersonic molecular beam techniques. Spectroscopic parameters of these complexes in the E0g+ ion-pair state, such as binding energies and several spectroscopic constants, have been determined. Most likely, the potential energy surfaces of the all RgI2(E) complexes under study present T-shaped minima. Vibrational and electronic predissociations of the RgI2(E) complexes were analyzed. Relative contributions of the different electronic predissociation channels and vibrational distributions of the decay products were determined. Possible mechanisms of the complexes decay are suggested and discussed