The Geometric Phase in Quantum Reaction Dynamics

Gert D. Billing, Satrajit Adhikari

Jiayu Huang, Brian K. Kendrick, Dong Hui Zhang

Ultracold chemical reactions involve collision temperatures approaching absolute zero, and for molecular systems that exhibit a barrierless and exoergic reaction path significant reactivity can occur. In addition, many molecules contain a conical intersection, and the associated geometric phase has been shown to significantly alter the outcome of ultracold reactions. Here we report a quantum dynamics study for the ultracold O + OH → H + O 2 reaction. An analysis of the scattering wave functions reveals explicitly the nature of the quantum interference between the direct and looping reaction pathways around the conical intersection and thus illustrates how the reaction proceeds under the control of the geometric phase for the first time. The wave function analysis should generalize to other ultracold reactions that contain a conical intersection. Our findings indicate that quantum control techniques such as an optical lattice trap or the initial state orientation may be effective in controlling the reactivity.

Arno Böhm, Ali Mostafazadeh, Hiroyasu Koizumi +2 more

Brian K. Kendrick, N. Balakrishnan

The role of the geometric phase effect in chemical reaction dynamics has long been a topic of active experimental and theoretical investigations. The topic has received renewed interest in recent years in cold and ultracold chemistry where it was shown to play a decisive role in state-to-state chemical dynamics. We provide a brief review of these developments focusing on recent studies of O + OH and hydrogen exchange in the H + H 2 and D + HD reactions at cold and ultracold temperatures. Non-adiabatic effects in ultracold chemical dynamics arising from the conical intersection between two electronic potential energy surfaces are also briefly discussed. By taking the hydrogen exchange reaction as an illustrative example it is shown that the inclusion of the geometric phase effect captures the essential features of non-adiabatic dynamics at collision energies below the conical intersection.

Arno Böhm

Brian K. Kendrick, Jisha Hazra, N. Balakrishnan

Quantum reactive scattering calculations for the hydrogen exchange reaction H+H_{2}(v=4,j=0)→H+H_{2}(v^{'}, j^{'}) and its isotopic analogues are reported for ultracold collision energies. Because of the unique properties associated with ultracold collisions, it is shown that the geometric phase effectively controls the reactivity. The rotationally resolved rate coefficients computed with and without the geometric phase are shown to differ by up to 4 orders of magnitude. The effect is also significant in the vibrationally resolved and total rate coefficients. The dynamical origin of the effect is discussed and the large geometric phase effect reported here might be exploited to control the reactivity through the application of external fields or by the selection of a particular nuclear spin state.