Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session K09: Molecular Structure and Collisions |
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Chair: Robert Forrey, Penn State University Room: Wisconsin Center 103DE |
Wednesday, May 29, 2019 2:00PM - 2:12PM |
K09.00001: Controlling the dynamics of cold molecular collisions James Croft, Naduvalath Balakrishnan The dynamics of many chemical processes are determined by the relative orientation of colliding molecules. Here, we report results of quantum dynamics calculations for cold collisions of rotationally excited HD with H$_2$, and examine how the collisional dynamics can be controlled by varying the initial alignment of the HD. Such control over the alignment of colliding molecules is now experimentally possible using the SARP method. Taking rotational quenching rates as an example we show that the rate can be maximised by aligning the HD along the relative collision axis and minimised by aligning the HD at the so called magic angle. [Preview Abstract] |
Wednesday, May 29, 2019 2:12PM - 2:24PM |
K09.00002: Laser driven production of antimatter molecules Mark Zammit, Michael Charlton, James Colgan, Svante Jonsell, Jeremy Savage, Dmitry Fursa, Igor Bray, Christopher Fontes, David Kilcrease, Peter Hakel, Jeffery Leiding, Eddy Timmermans Recent years have seen marked progress in the production of, and experimentation with, atomic antimatter in the form of antihydrogen, $\overline{\rm H}$. Now we investigate the feasibility of producing the anti-molecular hydrogen anion, $\overline{{\rm H}}_2^-$ (consisting of two anti-protons and a positron), in the laboratory. Utilizing reaction rates calculated here and from the literature, key processes are identified that could lead to anion production. The feasibility of these reactions are discussed in the context of present day and near future experimental capabilities. [Preview Abstract] |
Wednesday, May 29, 2019 2:24PM - 2:36PM |
K09.00003: Several levels of theory for description of isotope effects in ozone Dmitri Babikov We developed a multi-level theory for description of the intricate isotope effect in ozone. At 0th level of theory the role of molecular symmetry is taken into account. Although the important factors of 1/2 appear in seven different places in the formalism, this level of theory does not lead to any isotope effect. At the 1st level the effect of atomic masses is introduced to elucidate the roles of vibrational zero-point energies and rotational excitations. It is found that averaging over thermal distribution smooths isotopic differences and leads to a small net effect. At the 2nd level the process is assumed to proceed through independent diabatic ro-vibrational channels, which permits to determine contribution of shape resonances populated by tunnelling. Resultant isotope effects do not look like experiment and the rate coefficient is too small. At the 3rd level the role of Feshbach resonances is determined, by accurate close-coupling calculations using hyper-spherical coordinates, adaptive grids, sequential diagonalization truncation technique and complex absorbing potential. Comparison with experiment is presented. Refs: J. Phys. Chem. A 122, 9177 (2018); J. Chem. Phys. 149, 164302 (2018). [Preview Abstract] |
Wednesday, May 29, 2019 2:36PM - 2:48PM |
K09.00004: Spectroscopy of trapped molecular ions augmented with internal state control Ivan Antonov, Patrick Stollenwerk, Sruthi Venkataramanababu, Brian Odom 1-photon photodissociation spectrum of the 2$^{\mathrm{2}}\Pi $-X$^{\mathrm{2}}\Sigma $ transition of SiO$^{\mathrm{+}}$ was recorded in the range 212-232 nm. The SiO$^{\mathrm{+}}$ ions were loaded into RF trap and sympathetically cooled by Ba$^{\mathrm{+}}$ ions. Spectrally pulse-shaped broadband femtosecond laser was used to cool and control internal states of SiO$^{\mathrm{+}}$ via B$^{\mathrm{2}}\Sigma $ - X$^{\mathrm{2}}\Sigma $. The internal state control of SiO$^{\mathrm{+}}$ was used to probe the photodissociation spectrum for the range of N'' $=$ 0 - 65 and v'' $=$ 0 - 1 and to assign the observed transitions. The previously unobserved 2$^{\mathrm{2}}\Pi $ state of the SiO$^{\mathrm{+}}$ was experimentally characterized. It was found that the 2$^{\mathrm{2}}\Pi $ state undergoes predissociation with the lifetime of 10 ps, much faster than its predicted radiative lifetime of 77 ns and sufficiently slow to resolve the rotational structure in the recorded spectrum. The photodissociation of SiO$^{\mathrm{+}}$ via the 2$^{\mathrm{2}}\Pi $-X$^{\mathrm{2}}\Sigma $ transition was used to probe the ground state population and to study the cooling and state control mechanism. Direct control of internal states of molecules can be an efficient tool for molecular spectroscopy when the state density is extremely low, e.g. at very low concentrations or for remote regions of molecular potential. Potential applications will be discussed. [Preview Abstract] |
Wednesday, May 29, 2019 2:48PM - 3:00PM |
K09.00005: Formation of SiO$^+$ and CS$^+$ cations by radiative association James Babb, Robert Forrey, Brendan McLaughlin Rate constants for the formation of SiO$^+$ by radiative association are calculated using accurate molecular data. The ab initio potential curves and transition dipole moment functions were obtained using the multi-reference configuration interaction approach with the Davidson correction (MRCI+Q) and aug-cc-pCV5Z basis sets. The rate constants include both direct and indirect (inverse rotational predissociation) formation processes. The indirect processes are evaluated for conditions of local thermodynamic equilibrium (LTE) and also in the non-LTE limit of zero radiation temperature and atomic density. Phenomenological rate constants for SiO$^+$ formation in realistic astrophysical environments are expected to lie between these limiting cases. We compare the results for SiO$^+$ with those for the isoelectronic system CS$^+$, for which we have calculated the molecular data similarly to that for SiO$^+$. [Preview Abstract] |
Wednesday, May 29, 2019 3:00PM - 3:12PM |
K09.00006: Feshbach resonances in the ultracold 6Li-173Yb mixtures Hui Li, Ming Li, Svetlana Kotochigova The LiYb molecule is of current experimental interest due to its spin doublet ground state with both electric and magnetic dipole moments. Here, we develop a theoretical model to predict the location and width of Feshbach resonances in $^6$Li-$^{173}$Yb mixtures at ultracold temperatures by taking into account $R$-dependent hyperfine couplings. By using the non-relativistic configuration-interaction valance-bond (CI-VB) method, we, first, compute the hyperfine coupling constants as functions of internuclear separation. The short-range modification of the hyperfine couplings leads to narrow Feshbach resonances. Then we present quantum scattering calculations using the state-of-art {\it ab~initio} $^2\Sigma^+$ molecular potential, which has been adjusted to reproduce spectroscopic bound-state measurements. The calculated resonance widths, although small, are comparable to some of the successfully observed resonances in RbSr [1]. Finally, we describe the properties of the predicted $^6$Li$^{173}$Yb Feshbach resonances, offering a guide for current experimental measurements. [1] B. Vincent, C. Alessio, P. Benjamin, R. Lukas, S. Florian, P. S. \.{Z}uchowski and J. M. Hutson, Nature Phys. {\bf 14}, 881 (2018). [Preview Abstract] |
Wednesday, May 29, 2019 3:12PM - 3:24PM |
K09.00007: Signature of the $s$-wave regime high above ultralow temperatures Robin C\^ot\'e, I. Simbotin Resonant exchange scattering plays a key role in many-body dynamics and transport phenomena (e.g., spin, charge, or excitation diffusion). We show that the $s$-wave contribution to the resonant exchange cross section for such processes, generally thought to contribute mainly in the ultracold (or Wigner) regime, dictates the overall cross section over a wide range of energies. We derive a simple analytical expression for the cross section and explain its applicability for energies high above the Wigner regime. We also discuss its relationship to the classical capture (Langevin) cross section, and apply it to three very different resonant processes; namely, resonant charge transfer, spin-flip, and excitation exchange. Our new result explains large variations for different isotopes that cannot otherwise be accounted for by the small change in mass. The $s$-wave signature also allows to gain information about the Wigner regime from data obtained at much higher temperatures, which is especially advantageous for systems where the ultracold regime is not reachable. [Preview Abstract] |
Wednesday, May 29, 2019 3:24PM - 3:36PM |
K09.00008: Calculation of scattering resonances in ozone using stabilization method Elizaveta Grushnikova, Dmitri Babikov Study of the formation mechanism for atmospheric ozone helps to understand development of planetary atmosphere. We focus on anomalous mass-independent isotope effect. To understand the nature of isotope effect we consider all stages of ozone formation with commonly used mechanism at the low pressure regime - energy transfer (Lindemann) mechanism which involves metastable intermediate state O3*. O3* is described by scattering resonance in quantum mechanics. Particularly, scattering resonances can be calculated using of stabilization method of Clary. Stabilization approach implies that eigenvalues change as a functions of stabilization parameter (extension of the grid boundary). Based on quantum mechanical calculations of scattering resonances, kinetic rate coefficients were computed. Found resonance states were used for calculation of kinetics rate coefficients such as equilibrium and recombination coefficients for three pressure regimes (0.3, 30 and 3000 atm). Influence of pressure was estimated as well as contributions of other kinetic parameters - stabilization constant weight of each resonance, rotational, vibrational and electronic partition functions for molecule $^{\mathrm{686}}$O3. [Preview Abstract] |
Wednesday, May 29, 2019 3:36PM - 3:48PM |
K09.00009: Prospects for efficient sympathetic cooling of OH radicals by ultracold Sr atoms Ming Li, Alexander Petrov, Jacek K{\l}os, Svetlana Kotochigova There is great interest in direct cooling of molecules down to $\mu$K temperatures. One candidate molecule is the hydroxyl (OH) radical, which can not be laser cooled but is of interest to chemistry. A recent experiment~[1] has succeeded to translationally cool OH to 5 mK via evaporative cooling. Sympathetic cooling of molecules in collisions with laser-cooled atoms can assist further cooling down to $\mu$K. Here, we theoretically explore the translational cooling of OH in collisions with Sr. First, we computed the multi-dimensional potential surfaces of SrOH. Second, for coupled-channels calculations we add spin-orbit, Omega doubling, Coriolis, and hyperfine interactions to describe OH. We also include non-adiabatic couplings between the potential energy surfaces, which have conical intersections (CIs) in collinear geometries. Finally, we computed the ratio between the rate of elastic or momentum-changing collisions and the rate for inelastic or energy releasing collisions at various entrance channels and collision energies. The role of the CIs is also investigated. [1] B. K. Stuhl, M. T. Hummon, M. Yeo, G. Qu\'{e}m\'{e}ner, J. L. Bohn, and J. Ye, Nature, \textbf{492}, 396 (2012). [Preview Abstract] |
Wednesday, May 29, 2019 3:48PM - 4:00PM |
K09.00010: Mixed Quantum/Classical Theory (MQCT) to Study Inelastic Scattering of Molecules Bikramaditya Mandal, Dmitri Babikov Inelastic scattering of gas-phase molecules is important for analysis of molecular spectra observed by astronomers. These processes are rather complicated as one needs to have detailed description of state-to-state transition cross sections in a broad range of energy. Quantum mechanical treatment of these processes is computationally expensive while classical description is not always accurate. Solution is a mixed quantum/classical theory (MQCT) where translational motion (scattering) is treated classically whereas internal motion (rotation and/or vibration) is treated quantum mechanically. It makes the methodology computationally inexpensive, applicable even to larger molecules in broad range of collision energy. Computation of differential cross sections is also possible within MQCT using phase information to build the interference of partial waves. Moreover, MQCT can also provide some insight for the lower-energy regime dominated by scattering resonances. Detailed analysis of differential and integral cross sections for elastic and inelastic scattering of Na $+$ N$_{\mathrm{2}}$ is explored using this methodology, and accuracy is confirmed in a broad range of energy. [Preview Abstract] |
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