Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session P26: Nonadiabatic Dynamics in Cold and Utracold Collisions and Reactions IIIFocus Live
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Sponsoring Units: DCP Chair: Balakrishnan Naduvalath, University of Nevada - Las Vegas |
Wednesday, March 17, 2021 3:00PM - 3:36PM Live |
P26.00001: Nonadiabatic dynamics of NO colliding with atoms and molecules. Invited Speaker: Gerrit Groenenboom The nitric oxide (NO) radical has been a paradigm molecule in cold and controlled collision studies for many years. Its 2Π electronic ground state is spatially degenerate. This results in a linear Stark effect which allows manipulation of a molecular beam of NO with electric fields. In a Stark-decelerator experiment in Nijmegen, integral and differential cross sections for collisions of NO with helium were observed at collision energies down to 0.2 cm-1 with an energy resolution of 0.02 cm-1 [1]. Because of the electronic (near) degeneracy, nonadiabatic couplings are strong and we use diabatic states in the quantum scattering calculations. This approach is well known, but because of the unprecedented experimental resolution and the low collision energies, we have re-visited several common approximations in our calculations. We computed potential energy surfaces at the CCSDT(Q) level and explored nonadiabatic effects beyond the usual two-state model. In particular, we developed a method to estimate the diagonal Born-Oppenheimer correction (DBOC) and determined its effect on cross sections. The DBOC from electronic structure codes (we used CFOUR) diverges for open-shell systems. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P26.00002: Stereodynamics of rotational quenching in cold molecular collisions Masato Morita, Qian Yao, Changjian Xie, Hua Guo, Balakrishnan Naduvalath Stereodynamics of cold molecular collisions is an emerging area in cold and ultracold chemistry. Recently, Zare’s group examined the rotational quenching of HD in cold collisions with H2, D2 and He by combining the co-expansion of the colliding species and preparation of HD alignment and orientation with Stark-induced Adiabatic Raman Passage (SARP), and addressed the stereodynamic control of the angular distribution of inelastically scattered HD near 1K. In this study, we examine the possibility of stereodynamic control of rotational quenching in a strongly interacting system HCl+H2 in the cold energy regime. Using quantum scattering calculations on an accurate 6D potential energy surface, we show that robust control of collision outcome is possible even when multiple shape-resonances coexist in a narrow energy range, indicating that cold stereochemistry offers great promise for many molecules beyond simple systems. Also, for HD+He, we demonstrate that an interplay of resonances from an l=1 and l=2 partial waves governs collision outcome than a single l=2 partial wave attributed in the experiment. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P26.00003: Prediction of a Feshbach Resonance in the Below-the-Barrier Reactive Scattering of Vibrationally Excited HD with H Boyi Zhou, Benhui Yang, Balakrishnan Naduvalath, Brian Kendrick, Phillip C Stancil Triatomic collision processes have played an important role in quantum dynamics, as they can give valuable insight into the chemical reaction mechanism. In this work, quantum reactive scattering calculations on the vibrational quenching of HD due to collisions with H were carried out employing an accurate potential energy surface. The state-to-state cross sections for the chemical reaction HD (v = 1, j = 0) + H → D + H2 (v′ = 0, j′) at collision energies between 1 and 10,000 cm-1 are presented, and a Feshbach resonance in the low-energy regime, below the reaction barrier, is observed for the first time. The resonance is attributed to coupling with the vibrationally adiabatic potential correlating to the v = 1, j = 1 level of the HD molecule, and it is dominated by the contribution from a single partial wave. The properties of the resonance, such as its dynamic behavior, phase behavior, and lifetime, are discussed. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P26.00004: Stereodynamics of D2 (v = 2, j = 2) → D2 (v = 2, j = 0) cold collision with He reveals resonance Haowen Zhou, William Perreault, Nandini Mukherjee, Richard N Zare By preparing D2 in the rovibrational eigenstate (v = 2, j = 2) with three different bond axis orientations using Stark-induced adiabatic Raman passage (SARP), we study the stereodynamics of rotational relaxation of D2 (v = 2, j = 2) → D2 (v = 2, j = 0) via collision with ground-state He. The collision temperature is cooled to a few degrees Kelvin by coexpanding the colliding partners in a single supersonic beam, thus limiting the input orbital states to l = 0, 1, 2. Specifically, the D2 bond axis is prepared either parallel, perpendicular, or in a coherent superposition of two orientations at 45° with respect to the collision velocity. We observed marked stereodynamic features for each orientation of the D2 bond axis. Partial wave analysis of the rotationally relaxed D2 (v = 2, j = 0) angular distribution shows dominance of the even outgoing orbitals l′ = 0, 2, 4, which strongly suggests a scattering resonance for the l = 2 input orbital. The l = 2 resonance is further supported by comparing the collision temperature distribution with the centrifugal barrier. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P26.00005: Novel Dynamics in Ultracold Inelastic Li2 - Rare Gas Collisions Simon Rothman, William Jasmine, George C McBane, Brian Stewart We have modeled the collision of lithium dimer with the rare gases Ne and Xe at collision speeds as low as 30 cm/s using classical mechanics on ab initio potentials. In these very low energy collisions, the attractive part of the potential leads to Langevin capture, with a cross section that rises with declining collision speed according to σLangevin ∼ vrel-2/3. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P26.00006: Adsorption dynamics of cold atoms: Decay of surface Feshbach resonances Dennis Clougherty The adsorption of a cold atom to a surface has been described by Clougherty and Kohn in terms of the decay of overlapping Feshbach resonances involving the incident atom channel with the adsorbed atom accompanied by excitations of the solid. Since this resonance condition can be tuned with applied stress, adsorption on a 2D material might be controlled by tension. The dynamics of adsorption of cold atoms on 2D materials is studied theoretically using the Dirac-Frenkel time-dependent variational principle with a trial state consisting of a time-dependent linear combination of the incident atom and a bound atom with single-phonon-added coherent states. The effect of tension on the adsorption rate is the principal focus of this study. Tensile stress (1) reduces the strength of atom-surface potential at long distances, consequently tuning the scattering length; and (2) increases the transverse speed of sound in the 2D material, decreasing the phonon density of states. Both of these effects will alter the adsorption rate. Thus, applied tensile stress might in principle be used to control cold atom adsorption on 2D materials. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P26.00007: Understanding Magnetic Feshbach Resonances in Collisions of Ultracold NaK with K Matthew Frye, Jeremy Hutson Magnetic Feshbach resonances are a key feature in the scattering of ultracold atoms and have been pivotal in their study. Now that ultracold molecules can be made, their scattering properties are of great interest, both with themselves and with ultracold atoms. Feshbach resonances have been observed in ultracold collisions of Na40K with 40K by Zhao and coworkers in Shanghai [Yang et al Science 363, 261], and if these resonances can be understood they will provide insight into and control over these collisions. We use extended results from the Shanghai group to arrive at a detailed model for a low-field group of resonances and suggest possible interpretations for another group of resonances. The states causing such resonances have often been assumed to be highly complicated or even chaotic in nature due to the deep and anisotropic short-range potentials. However, our suggested interpretation is based on weakly bound long-range states which are highly ordered and relatively simple. Such states and corresponding low-field Feshbach resonances may be expected in other similar alkali atom+diatom collision systems. |
Wednesday, March 17, 2021 4:48PM - 5:24PM Live |
P26.00008: Recent development of state-to-state quantum reactive scattering theory Invited Speaker: Zhigang Sun Development about efficient and accurate theory is fundamental problem in theoretical |
Wednesday, March 17, 2021 5:24PM - 6:00PM Live |
P26.00009: Full quantum state-to-state mapping of molecular ion collisions via electron-ion coincidence spectroscopy Invited Speaker: Ed Narevicius Exothermic inelastic and reactive process with strong interactions usually lead to a large number of accessible quantum states in the product channels. The final quantum state distribution caries unique information about the microscopic collision mechanism. However, experimental measurement of a complete quantum state distribution in many channels remains challenging and rare. |
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