Speaker: Olivier Dulieu (Laboratoire Aimé Cotton, CNRS, France) Title: Electronic structure of alkali dimers and trimers. Prospects for alignment and orientation effects. Time: Today, 10.15 to 11.00 Place: Fysisk Auditorium Abstract: The rapid development of experimental techniques to produce cold and ultracold molecules [1] opens the ways to manipulate them or to control their formation dynamics using external fields, and to explore their interactions with surrounding particles. In most cases, the detailed knowledge of the internal molecular structure is required to guide such studies and to interpret their results. For several years now our group carries out systematic theoretical investigations on alkali molecular systems, using a quantum chemistry approach based on pseudopotentials for atomic core representation, Gaussian basis sets, and effective potentials for core polarization [2]. Potential curves and permanent and transition dipole moments have been obtained for all alkali pairs, both homonuclear and heteronuclear [2, 3], which are relevant for ultracold molecule formation processes. Calculations for ionic species like MgH+ have been also performed. The manipulation of polar bialkali molecules with electrostatic or strong off-resonant laser fields is governed by their dipole moment and their static polarizability. We computed the static dipole polarizability tensor for all bialkali pairs [4], and for alkali hydrides. We will present scenarios for the permanent alignment of ultra-cold heteronuclear molecules [4], based on combinations of static electric fields and strong laser fields [5]. Once ultracold molecular samples are dense enough, the interaction between atoms and molecules become observable [6]. We present preliminary results on the calculation of potential energy surfaces for heavy alkali trimers (Cs3) at arbitrary geometries and symmetries. Using effective core potentials, it is possible to carry out full configuration interaction calculations for the valence electrons and hence accurately take into account all electronic interactions [7]. Finally, we present a new investigation of the dynamics of the H2-H- complex, and discuss the possible formation of H3- in the interstellar medium [8]. [1] O. Dulieu and C. Gabbanini, Reports on Progress in Physics, 72, 086401 (2009) [2] M. Aymar and O. Dulieu, J. Chem. Phys. 122, 204302 (2005) [3] M. Aymar and O. Dulieu, Mol. Phys. 105, 1733 (2007) [4] J. Deiglmayr, M. Aymar, R. Wester, M. Weidemüller, and O. Dulieu, J. Chem. Phys. 129, 064309 (2008) [5] B. Friedrich and D. Herschbach, J. Phys. Chem. A 103, 10280 (1999) [6] N. Zahzam et al, Phys. Rev. Lett. 96, 023202 (2006) ; P. Stanuum et al, Phys. Rev. Lett. 96, 0232021 (2006); [7] R. Guérout, P. Soldan, M. Aymar, J. Deiglmayr, O. Dulieu, Int. J. Quant. Chem., 109, 3387 (2009) [8] V. Kokoouline, M. Ayouz, R. GuÍ©rout, M. Raoult, J. Robert, O. Dulieu, arXiv: physics.atom-ph/ 0910.2330 Peter Staanum and Nicolai Nygaard Coffee, tea and bread rolls will be served at 10.05