Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session D02: Ultracold State-to-State Chemistry |
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Sponsoring Units: GFB Chair: Mike Tarbutt, Imperial College London Room: Grand A |
Tuesday, May 29, 2018 2:00PM - 2:30PM |
D02.00001: Quantum-state-controlled photodissociation of ultracold diatomic molecules Invited Speaker: Tanya Zelevinsky At ultracold temperatures, collisions and reactions of atoms and molecules exhibit quantum mechanical behavior, since only the selected quantum states of the reactants and products can participate. The breaking of a diatomic molecular bond by coherent light, or photodissociation, is a basic process that exhibits many quantum mechanical features when performed at ultralow energies. Photodissociation of diatomic strontium molecules is highly amenable to a high-precision experimental and theoretical treatment, and we discuss this “reverse collision” process in the regime of up to a few millikelvin, where the molecules are prepared in specific quantum states in an optical lattice at microkelvin temperatures. We demonstrate coherent superpositions and matter-wave interference of the reaction products, effects of barrier tunneling, an ability to control the process with weak magnetic fields, and a transition from quantum mechanical to quasiclassical behavior as the kinetic energy of the photofragments is increased. Ultracold photodissociation additionally provides an excellent test of quantum chemistry models in the scattering continuum, is well suited for experimental studies of scattering continua that are less amenable to theory, and serves as a coherent source of monoenergetic atomic or molecular fragments. [Preview Abstract] |
Tuesday, May 29, 2018 2:30PM - 3:00PM |
D02.00002: State-to-state chemistry for three-body recombination in an ultracold rubidium gas Invited Speaker: Johannes Hecker-Denschlag Experimental investigation of chemical reactions with full quantum state resolution for all reactants and products has been a long-term challenge. We have recently developed an experimental method for detecting molecules in a quantum state resolved way with unprecedented resolution, which we can use to study chemical reactions. As a benchmark reaction, we investigate three-body recombination of ultracold Rb atoms, where two atoms combine to form a Rb2 molecule while the third atom carries away part of the released binding energy. Initially the atoms are prepared in a well-defined internal quantum state. After the reaction we state-selectively ionize the produced molecules with a resolution of about 5 MHz such that most molecular quantum states can be spectroscopically distinguished. Our results allow for formulating propensity rules for the distribution of products. Furthermore we have developed a theoretical model that predicts many of our experimental observations. The scheme can readily be adapted to other species and opens a door to detailed investigations of inelastic or reactive processes. [Preview Abstract] |
Tuesday, May 29, 2018 3:00PM - 3:30PM |
D02.00003: Cold Chemistry with Cold Molecules Invited Speaker: Ed Narevicius I will discuss our efforts towards reaching ultra-cold temperatures with trapped molecules where molecular beams carrying both cold molecules and atoms have been decelerated and trapped in a permanent magnetic trap. I will present our plans and prospects of further cooling via evaporation or collisions with laser cooled atoms. In the second part of my talk I will focus on cold collisions with cold molecular partners that have been magnetically merged in order to reach collisions temperatures of ~10 mK. I will show that quantum phenomena dominates collisions in this cold regime and discuss the importance off molecular degrees of freedom on cold reactions. I will present our latest results where low energy collisions have been imaged using the Velocity Map Imaging technique allowing us to observe rotational quantum state selective inelastic scattering as well as diffraction oscillations that occur in cold elastic collisions. [Preview Abstract] |
Tuesday, May 29, 2018 3:30PM - 4:00PM |
D02.00004: Taming molecular collisions Invited Speaker: Bas van de Meerakker The study of molecular collisions with the highest possible detail has been an important research theme in physical chemistry for decades. Over the last years we have developed methods to get improved control over molecules in a molecular beam. With the Stark decelerator, a part of a molecular beam can be selected to produce bunches of molecules with a computer-controlled velocity and with longitudinal temperatures as low as a few mK. The molecular packets that emerge from the decelerator have small spatial and angular spreads, and have almost perfect quantum state purity. These tamed molecular beams are excellent starting points for high-resolution crossed beam scattering experiments. \\ \\ I will discuss our most recent results on the combination of Stark deceleration and velocity map imaging. The narrow velocity spread of Stark-decelerated beams results in scattering images with an unprecedented sharpness and angular resolution. This has facilitated the observation of diffraction oscillations [1,2] in the state-to-state differential cross sections for collisions of NO with rare gas atoms, the observation of scattering resonances at low-energy inelastic NO-He [3] and NO-H2 [4] collisions that reveal the influence of individual partial waves to the scattering dynamics, and product-pair correlations for bimolecular scattering processes [5]. \\ \\ $[1]$ A. von Zastrow et al., Nature Chemistry 6, 216 (2014)\\ $[2]$ J. Onvlee et al., Nature Chemistry 9, 226 (2017)\\ $[3]$ S. Vogels et al., Science 350, 787 (2015)\\ $[4]$ S. Vogels et al., Nature Chemistry (in press, 2018), DOI: 10.1038/s41557-018-0001-3\\ $[5]$ Z. Gao et al., Nature Chemistry (in press, 2018), DOI: 10.1038/s41557-018-0004-0 [Preview Abstract] |
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