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 D07: Electron-Molecule, Atom-Molecule, and Atom-Atom Collisions |
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Chair: Svetlana Kotochigova, Temple University Room: Grand D |
Tuesday, May 29, 2018 2:00PM - 2:12PM |
D07.00001: Semiclassical initial value representation for multimode calculation of dissociative electron attachment processes Harindranath Ambalampitiya, Ilya Fabrikant Dissociative electron attachment (DEA) to polyatomic molecules plays an important role in a vast variety of chemical processes that happen in nature and in industrial world. DEA calculations performed so far [1] were done either in approximation of one vibrational mode or in the local approximation which describes the nuclear motion in the intermediate resonance state by an effective Schroedinger equation with a local complex potential. In the present paper we develop a multimode theory which goes beyond the local approximation by employing the semiclassical initial value representation [2] for calculation of matrix elements of the Green operator for the nuclear motion. We apply this method to calculation of DEA to the CF$_3$Cl molecule with inclusion of the C-Cl symmetric stretch mode and the CF$_3$ umbrella mode. $^1$ I. I. Fabrikant \textit {et al.}, Adv. At., Mol.,Opt. Phys {\bf 66}, 545 (2017). $^2$ W. H. Miller, J. Phys. Chem. A {\bf 105}, 2942 (2001). [Preview Abstract] |
Tuesday, May 29, 2018 2:12PM - 2:24PM |
D07.00002: Elastic Scattering of Low Energy Electrons from Acetonitrile (CH$_{\mathrm{3}}$CN). Mateusz Zawadzki, Murtadha Khakoo Experimental differential cross sections for low energy electron scattering from acetonitrile, using the relative flow technique with helium [1], will be presented. The cross sections were taken at incident energies of 0.5 eV to 30 eV for scattering angles of 10$^{\mathrm{o}}$ to 130$^{\mathrm{o}}$ using a moveable aperture gas target source[1]. The results will be compared to the existing Schwinger multi-channel calculations of Maioli and Bettega [2]. [1] M. A. Khakoo, K. Keane, C. Campbell, N. Guzman and K. Hazlett, J. Phys. B: At. Mol. Opt. Phys. \textbf{40} 3601 (2007). [2] S. Maioli and M. H. F. Bettega, Eur. Phys. J. \textbf{D}. \textbf{71}, 322 (2017). [Preview Abstract] |
Tuesday, May 29, 2018 2:24PM - 2:36PM |
D07.00003: Non-Reactive Atom-Molecule Scattering in Support of a Cold-Atom Based UHV Pressure Sensor Constantinos Makrides, Eite Tiesinga The operation of a cold-atom vacuum sensor depends critically on the ability to characterize the collision between background gases in the vacuum with trapped sensor atoms, whose ejection from a shallow trap within the vacuum can be mapped to the pressure of the vacuum. The target pressure ranges are fully within the Ultra-High Vacuum (UHV) and into the Extreme-High-Vacuum (EHV) regime, where presently there is a lack of a primary standard. The effect of background molecules on the lifetime of trapped ultracold atoms was estimated in early experiments with ultracold gases; However, exact knowledge of the collisional properties between the constituents might prevent the realization of a cold atom vacuum sensor. Our goal here is to compute these key atom-molecule scattering properties by solving the coupled channels equations. We use H$_2$ and lithium as the constituents in our calculations, as H$_2$ is the most abundant molecule to be found in a vacuum and lithium is currently being utilized as a sensor atom in a realization of such a device at NIST. Specifically, we will show the cross-sections and thermalized rate for this collision pair with careful attention to the uncertainties in our approach. [Preview Abstract] |
Tuesday, May 29, 2018 2:36PM - 2:48PM |
D07.00004: Universal Scattering with Ultracold Polar Molecules in Optical Potentials Alexander Petrov, Hui Li, Constantinos Makrides, Ming Li, Svetlana Kotochigova Interactions between atoms and molecules are controlled by their attractive long-range van-der-Waals potentials as well as their short-range exchange and repulsive potentials. Here, we determine the ultracold inelastic and elastic scattering rate coefficients for a large class of polar molecules in their lowest vibrational state with their constituent atoms using universal scattering theory. Universal scattering is solely determined by the van-der-Waals, dispersion interaction, which in turn is defined by the dynamic polarizability of the atom and molecule as a function of imaginary frequency. We examine two different approaches to calculate the dynamic polarizability: 1) a {\it perturbation-theory-based} method that uses relativistic potentials and transition dipole moments, and 2) a non-relativistic {\it coupled cluster polarization propagator} method. We evaluate the strengths and weaknesses of these methods. Finally, we compare our inelastic rates coefficients with experimental measurements and exact quantum-mechanical calculations, where available. Our goal is to provide a better understanding of the limits of the universal scattering model at ultra-low temperatures and, in particular, the degree to which short-range potentials are important. [Preview Abstract] |
Tuesday, May 29, 2018 2:48PM - 3:00PM |
D07.00005: Nonadiabatic effects in ultracold trimer molecules Hui Li, Ming Li, Alexander Petrov, Svetlana Kotochigova It has become possible to investigate chemical reactions between small molecules at temperatures well below 1 mK, where quantum effects and threshold phenomena begin to dominate the collision process. Recently, it has been demonstrated [1] that the collisional complexes of the ultracold alkali-metal trimers and tetrimers have conical intersections, lines of degeneracy of the potential surfaces. These intersections allow efficient nonadiabatic transitions between surfaces. The goal of the current study is to investigate conical intersection that occurs in the LiNaLi collisional complex. We, first, focus on the {\it ab~initio} calculation of the lowest $^2A_1$ and $^2B_1$ adiabatic potential surfaces and the corresponding nonadiabatic coupling function between them. The diabatic surfaces and their coupling are produced through a diabatization process. Then the potential landscape including the conical intersection is analyzed. [1]P. S. \.{Z}uchowski and J. M. Hutson, Phys. Rev. A {\bf 81}, 060703(R) (2010). [Preview Abstract] |
Tuesday, May 29, 2018 3:00PM - 3:12PM |
D07.00006: Quantum tunneling isotope exchange reaction H$^2$ + D$^-$ $\rightarrow$ HD + H$^-$ Chi Hong Yuen, Mehdi Ayouz, Eric Endres, Olga Lakhamanskaya, Roland Wester, Viatcheslav Kokoouline The tunneling reaction H$_2$ + D$^-$ $\rightarrow$ HD + H$^-$ was studied in a recent experimental work at low temperatures (10, 19, and 23~K) by Endres {\it et al.}[1]. An upper limit of the rate coefficient was found to be about 10$^{-18}$ cm$^3$/s. In the present study, reaction probabilities are determined using the ABC program developed by Skouteris {\it et al.}[2]. The probabilities for ortho-H$_2$ and para-H$_2$ in their ground rovibrational states are obtained numerically at collision energies above 50~meV with the total angular momentum $J$ = 0 - 15 and extrapolated below 50~meV using a WKB approach. Thermally averaged rate coefficients for ortho- and para-H$_2$ are obtained; the largest one, for ortho-H$_2$ is about $3.1\times10^{-20}$ cm$^3$/s, which agrees with the experimental results. [1] Endres {\it et al.} PRA 95, 022706 (2017) [2] Skouteris {\it et al.} Comput. Phys. Commun. 133, 128 (2000) [Preview Abstract] |
Tuesday, May 29, 2018 3:12PM - 3:24PM |
D07.00007: Production and Characterisation of a Cryogenic Water Beam for Ion-Molecule Chemistry Gary Chen, Tiangang Yang, Arthur Suits, Wesley Campbell, Eric Hudson Despite the fact that chemical reactions between polar neutral molecules and ions in cold, dilute interstellar media are dominant, key properties, such as product branching ratios and reaction rates, are poorly understood. A grasp of these reaction values at cryogenic temperatures remains a challenge to current theory. ~Towards these goals, we have built a cryogenic beam source to be used in conjunction with a linear quadrupole trap and time of flight mass spectrometer to probe reactions between cold neutral molecules and trapped ions. We report the production and characterisation of a cryogenic water beam as well as observed water chemistry with both beryllium and carbon ions at low reaction temperatures. [Preview Abstract] |
Tuesday, May 29, 2018 3:24PM - 3:36PM |
D07.00008: Optical fields to control ultracold atomic molecular collisions Nadia Bouloufa-Maafa, Andrea Orban, Olivier Dulieu Research focusing on the formation of ultracold atomic and molecular quantum gases is a continuously expanding field due to its envisioned applications such as quantum-controlled chemistry or quantum simulation. The aim of our theoretical work is to find ways to suppress inelastic or reactive processes between colliding particles in ultracold quantum gases. Using a laser field detuned to the blue of a relevant transition, we propose to couple the initial colliding particle state to a repulsive excited one, thus preventing the particles to come close to each other. This ``blueshielding'' technique is applied for ultracold quantum gases, close to quantum degeneracy. Due to the extremely small collisional energies it is possible to address a single repulsive channel thus ensuring a full control of the suppression efficiency. We will present our results in case of the39K133Cs molecule. $[1]$ A. Orban.et al. Phys. Rev. A, \textbf92, 265 (2015). $[2]$ A. Orban.et al. Phys. Rev. A,\textbf{92}, 265 (2015). [Preview Abstract] |
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