Pavel Soldán

Quantum dynamics of ultracold Na + Na2 collisions

Ultracold collisions between spin-polarized Na atoms and vibrationally excited Na2 molecules are investigated theoretically, using a reactive scattering formalism (including atom exchange). Calculations are carried out on both pairwise additive and nonadditive potential energy surfaces for the quartet electronic state. The Wigner threshold laws are followed for energies below 10(-5) K. Vibrational relaxation processes dominate elastic processes for temperatures below 10(-3)-10(-4) K. For temperatures below 10(-5) K, the rate coefficients for vibrational relaxation (v=1-->0) are 4.8x10(-11) and 5.2x10(-10) cm(3) s(-1) for the additive and nonadditive potentials, respectively. The large difference emphasizes the importance of using accurate potential energy surfaces for such calculations.

A study of the role of ion-molecule chemistry in the formation of sporadic sodium layers

Over two campaigns in 1998 and 1999, multiple sporadic sodium events were observed by the Arecibo Observatory sodium density lidar while simultaneously monitoring the plasma density using the incoherent scatter radar. In this paper, we test the theoretical explanation proposed by Cox and Plane (1998) where Na + in a plasma layer is neutralized via an ion–molecule mechanism to form a sporadic sodium layer. A particular challenge is to interpret observations made in a Eulerian frame of observation where the spatial and temporal characteristics of events cannot easily be separated. The reaction scheme in the original mechanism is modi=ed to include the reactions NaO + +N2 → Na + ·N2 +O and NaO + +O2 → Na + +O3, following the results of theoretical quantum calculations. Six unique case studies of sporadic sodium layers are presented here, and excellent agreement between simulation and observations was obtained for =ve of them. c � 2002 Published by Elsevier Science Ltd.

Molecule formation in ultracold atomic gases

This review describes recent experimental and theoretical advances in forming molecules in ultracold gases of trapped alkali metal atoms, both by magnetic tuning through Feshbach resonances and by photoassociation. Molecular Bose–Einstein condensation of long-range states of both boson dimers and fermion dimers was achieved in 2002–2003. Condensates of boson dimers were found to be short-lived, but long-lived condensates of fermion dimers have been produced. Signatures of triatomic and tetraatomic molecules have recently been observed. Both homonuclear and heteronuclear molecules have been formed by photoassociation, mostly in very high vibrational levels. Recent attempts to produce ultracold molecules in short-range states (low vibrational levels) are described. Experimental and theoretical work on collisions of ultracold molecules is discussed. 1. Introduction 498 2. Basic properties of ultracold atomic gases 499  2.1. Bosons and fermions 499  2.2. Hyperfine structure 499  2.3. Trapping and cooling 500  2.4. Bose–Einstein condensation and Fermi degeneracy 501  2.5. Scattering lengths 502  2.6. Feshbach resonances 503 3. Molecules formed by Feshbach resonance tuning 506  3.1. Dimers of bosonic atoms 506  3.2. Dimers of fermionic atoms 508  3.3. Heteronuclear Feshbach resonances 511  3.4. Triatomic and larger molecules 512 4. Molecules formed by photoassociation 512  4.1. Photoassociation in Bose–Einstein Condensates 514  4.2. Coherent control 515  4.3. Molecules in low vibrational states 516 5. Molecules in optical lattices 517 6. Collisions of ultracold molecules 519 7. Conclusions 521 Acknowledgments 522 References 522

Quantum Dynamics of UltracoldNa+Na2Collisions

Ultracold collisions between spin-polarized Na atoms and vibrationally excited Na2 molecules are investigated theoretically, using a reactive scattering formalism (including atom exchange). Calculations are carried out on both pairwise additive and nonadditive potential energy surfaces for the quartet electronic state. The Wigner threshold laws are followed for energies below 10(-5) K. Vibrational relaxation processes dominate elastic processes for temperatures below 10(-3)-10(-4) K. For temperatures below 10(-5) K, the rate coefficients for vibrational relaxation (v=1-->0) are 4.8x10(-11) and 5.2x10(-10) cm(3) s(-1) for the additive and nonadditive potentials, respectively. The large difference emphasizes the importance of using accurate potential energy surfaces for such calculations.

Ultracold Li + Li2 collisions: bosonic and fermionic cases.

We have carried out quantum dynamical calculations of vibrational quenching in Li + Li(2) collisions for both bosonic (7)Li and fermionic (6)Li. These are the first ever such calculations involving fermionic atoms. We find that for the low initial vibrational states considered here (v < or = 3), the quenching rates are not suppressed for fermionic atoms. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states.

Molecular collisions in ultracold atomic gases

It has recently become possible to form molecules in ultracold gases of trapped alkali metal atoms. Once formed, the molecules may undergo elastic, inelastic and reactive collisions. Inelastic and reactive collisions are particularly important because they release kinetic energy and eject atoms and molecules from the trap. The theory needed to handle such collisions is presented and recent quantum dynamics calculations on ultracold atom–diatom collisions of spin-polarized Li + Li2, Na + Na2 and K + K2 are described. All these systems have potential energy surfaces on which barrierless atom exchange reactions can occur, and both inelastic and reactive rates are very fast (typically k inel > 10-10 cm3 s−1 in the Wigner regime).

On the long-range and short-range behavior of potentials from reproducing kernel Hilbert space interpolation.

The short-range and long-range asymptotic behavior of potential functions obtained from the reciprocal power reproducing kernel Hilbert space interpolation procedure [Ho and Rabitz, J. Chem. Phys. 104, 2584 (1996)] is analyzed. In the short-range region, the potential functions are polynomial in form: the method should not be used for extrapolation in this region. General formulae for the short-range and long-range expansion coefficients are presented. Potentials for He-Ar+ are discussed as examples.

Ultracold quantum dynamics: spin-polarized K + K_2 collisions with three identical bosons or fermions

We have developed a new potential energy surface for spin-polarized K(

Ultracold collisions involving heteronuclear alkali metal dimers

^2

Ultracold Rb-OH Collisions and Prospects for Sympathetic Cooling

S) + K