High-Resolution Spectroscopy of Heteronuclear Alkali Molecules: Structure and Dynamics

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This project involves the study of small molecules and how they interact with different atoms. In one experiment, a laser is used to give the molecules a precisely defined amount of vibrational and rotational energy. The molecules, which are in a small chamber, then have close encounters (collisions) with various other atoms (helium, argon, or potassium) that are also present in the chamber. A second laser is used to determine how the forces between the atoms and the molecules affect the vibration and rotation of the molecules. In a second experiment, lasers are used to measure the energy levels and other properties of the molecules. The results of both experiments will be compared with computer models based on the theory of quantum mechanics in order to test the understanding of how atoms and molecules interact. The proposed work is relevant to research in other areas of current interest, such as quantum computing and laser cooling of atoms and molecules. It will also contribute to the advanced education of several students. Three or four graduate students will write Ph.D. dissertations based on this work, and approximately six undergraduate students will participate in these projects during the summers through Lehigh University's REU (Research Experiences for Undergraduates) program. The specific activities that will be carried out involve measurements of the ro-vibrational energy levels of triplet states of NaCs and NaK, and the investigation of fine and hyperfine structure of these levels. The goal is to map out potential energy curves and transition dipole moments as functions of internuclear separation, to study spin-orbit and non-adiabatic coupling between states, and to use patterns of energy levels to investigate predissociation and other fundamental molecular interactions. In one such effort, the supported research group is developing a technique using quantum interference effects to determine detailed information about molecular perturbations. The interacting NaCs 11(0+) and 12(0+) states are being used as the test case. The group is currently extending their work to NaCs, because it is of interest for cooling and trapping. The large spin-orbit interactions in this molecule, which lead to strong perturbations and avoided crossings, provide interesting new challenges for both experiment and theory. In addition, the group's recent studies of rotationally inelastic collisions of alkali molecules have revealed a strong propensity for Delta J = even transitions in collisions of NaK molecules with either Ar or He atoms. However, this propensity is not observed in collisions of NaK with K atoms. The group has found that orientation is largely preserved in rotationally inelastic collisions of NaK with Ar or He, but is almost completely destroyed in collisions with potassium. The group's theoretical calculations are beginning to provide explanations for these results. Recent calculations predict strong J dependences in the probabilities for transfer of either orientation or alignment in rotationally inelastic collisions. Further experiments will test many of these predictions and provide stringent tests of molecular collision theory.