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Side-impact collisions of Ar with NO


In the realm of molecular collision dynamics, stereochemistry refers to the dependence of the collision outcome on the mutual orientation of the colliding partners. This may involve directed end-on collisions along a molecular bond axis or encounters in which the partner approaches the bond of an oriented molecule from the side. Using both experiment and theory, we show here that in the simplest case of an inelastic collision between an atom and a nearly homonuclear diatom, in which the two atoms have almost the same mass, the scattering dynamics are very distinct for impacts on either side of the molecule. By recording the direction of the scattered particles after the collision, we demonstrate that the intensity of products scattered in the forward direction, near parallel to the initial motion, can be substantially controlled and even maximized by altering the side-on orientation of the quantum state selected NO molecules that collide with Ar atoms. In addition, our findings provide valuable information about the preferred collision mechanism and reveal interesting quantum interference effects.

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Fig. 1: Schematic of the experimental configuration for bond-axis orientation measurements.
Fig. 2: Bond-axis orientation resolved experimental ion images and DCSs compared to the QM theoretical results.
Fig. 3: Comparison of the DCSs for side-on and end-on orientation.
Fig. 4: Illustrations of the scattering mechanism derived from the initial bond-axis oriented calculations.

Data availability

Experimental and computational data that support the findings of this study are available from the Oxford Research Archive (

Code availability

The Hibridon set of programs used for the QM calculations can be downloaded from The computer codes used for the data analysis are available from the corresponding author upon reasonable request.


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The support of the UK EPSRC (to M.B. via Programme Grant EP/L005913/1), and the Spanish Ministry of Science and Innovation (Grant No. CTQ2015-65033-P to F.J.A.) is acknowledged. P.G.J. acknowledges funding by the Fundación Salamanca city of culture and knowledge (programme for attracting scientific talent to Salamanca). We thank S. Stolte for many stimulating discussions throughout the course of some of the research described here.

Author information




The research project was conceived by M.B., C.G.H. and F.J.A. The experiments were performed by V.W. and C.G.H., and the data analysis was carried out by V.W. The theory was developed by M.B., V.W., P.G.J. and F.J.A., with the calculations performed by V.W. and P.G.J. The paper was written by M.B. and F.J.A., with all the authors contributing to discussions about the content of the paper.

Corresponding authors

Correspondence to Mark Brouard or Pablo G. Jambrina or F. Javier Aoiz.

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The authors declare no competing interests.

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Supplementary Information

Supplementary Methods, Supplementary analysis and Supplementary Figs. 1–8.

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Heid, C.G., Walpole, V., Brouard, M. et al. Side-impact collisions of Ar with NO. Nat. Chem. 11, 662–668 (2019).

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