Jesús Pérez Ríos

Molecular oxygen tetramer (O2)4: intermolecular interactions and implications for the epsilon solid phase

Recent data have determined that the structure of the high pressurephase of solid oxygen consists of clusters composed of four O2 molecules. This finding has opened the question about the nature of the intermolecular interactions within the molecular oxygen tetramer. We use multi- configurational ab initio calculations to obtain an adequate characterization of the ground singlet state of (O2)4 which is compatible with the non magnetic character of thephase. In contrast to previous suggestions implying chemical bonding, we show that (O2)4 is a van der Waals like cluster where exchange interactions preferentially stabilize the singlet state. However, as the clus- ter shrinks, there is an extra stabilization due to many-body interactions that yields a significant softening of the repulsive wall. We show that this short range behavior is a key issue for the understanding of the structure of �-oxygen.

Temperature independent quantum logic for molecular spectroscopy

This work is supported by Spanish MICINN Projects FIS2009-10061, FIS2010-22064-C02-02 and CTQ2007- 62898-BQU, CAM research consortium QUITEMAD S2009-ESP-1594, the Swiss National Science Foundation through the National Centre of Competence in Research \Quantum Science and Technology>, EU COST Action IOTA (MP1001), a FP7 Marie Curie fellowship (IEF- 2009-251913 MOLOPTLAT), and a JAE CSIC Fellow- ship.