Atom-diatom reaction dynamics at cold and ultracold temperatures

Brian K. Kendrick

Christian Schneider, Steven J. Schowalter, Kuang Chen +3 more

Philippe F. Weck, N. Balakrishnan

We review the recent progress achieved in the theoretical description of chemical reactions at low temperatures. In particular, we discuss the crucial role played by the van der Waals interaction potential in quantum-mechanical scattering calculations of atom–diatom collisions in the cold and ultracold regimes, where abstraction reactions proceed by tunnelling. The importance of zero-energy resonances in enhancing the reactivity in the zero-temperature limit is assessed. The impact of Feshbach resonances associated with the decay of metastable states of van der Waals complexes on reactive scattering is addressed through a series of examples. Finally, we discuss the sensitivity of the reaction dynamics to the topology of the van der Waals well. Importance of long-range interactions in chemical reactions at cold and ultracold temperaturesAll authorsPhilippe F. Weck & N. Balakrishnanhttps://doi.org/10.1080/01442350600791894Published online:22 February 2007Table Download CSVDisplay Table

F. D. Colavecchia, Gregory A. Parker, Russell T Pack

I. Simbotin

Theoretical results for ultracold atom-molecule collisions involving exoergic reactions are presented. Systems with a reaction barrier are considered; specifically, we report the results of extensive computations for D + H 2 and Cl + H2. We analyzed the extreme situation of translationally cold collisions between an atom and an internally hot molecule; namely, for D + H2 we explored the role played by the internal vibrational excitation of the diatomic target for initial states H2(υ) with υ = 0,1,2,…, 8. The υ-dependence of the zero-temperature limit of the reaction rate coefficient shows two distinct regimes: a barrier dominated regime for υ < 4, and a barrierless regime for υ > 4. Also, for highly excited initial states, the distribution over the final states of the products shows an approximate conservation of the internal vibrational energy. For Cl + H2 we studied in detail the isotopic effect by varying continuously the mass of H, which allowed us to find resonance effects in the threshold behavior of cross sections. These resonances are caused by long-lived van der Waals complexes (Cl···H2) which have vanishingly small binding energy, or by virtual states of the Cl···H 2 complex. ^

Dongzheng Yang, Jing Huang, Xixi Hu +2 more

A general and rigorous quantum method is proposed for studying capture dynamics between two diatomic molecules in full dimensionality. By solving the time-independent Schrödinger equation with proper boundary conditions, this method is ideally suited for studying quantum dynamics of cold and ultracold reactions. To illustrate its applicability, the capture dynamics between ultracold KRb molecules is characterized in full six dimensions for the first time using a first-principles based long-range interaction potential. The calculated capture rates for collisions involving distinguishable and indistinguishable 40K87Rb molecules are in good agreement with the experiment and exhibit clear Wigner threshold behaviors. Predictions for ultracold collisions between internally excited 40K87Rb suggest minor changes in the loss rate, consistent with experimental observations in similar systems.