Imaging rotational energy transfer: comparative stereodynamics in CO + N 2 and CO + CO inelastic scattering

• Published in: Physical chemistry chemical physics : PCCP 2023-07, Vol.25 (27), p.17828-17839
• Main Authors: Sun, Zhong-Fa, Scheidsbach, Roy J A, van Hemert, Marc C, van der Avoird, Ad, Suits, Arthur G, Parker, David H
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/D3CP02229C

State-to-state rotational energy transfer in collisions of ground ro-vibrational state CO molecules with N molecules has been studied using the crossed molecular beam method under kinematically equivalent conditions used for CO + CO rotationally inelastic scattering described in a previously published report (Sun , , 2020, , 307-309). The collisionally excited CO molecule products are detected by the same (1 + 1' + 1'') VUV (Vacuum Ultra-Violet) resonance enhanced multiphoton ionization scheme coupled with velocity map ion imaging. We present differential cross sections and scattering angle resolved rotational angular momentum alignment moments extracted from experimentally measured CO + N scattering images and compare them with theoretical predictions from quasi-classical trajectories (QCT) on a newly calculated CO-N potential energy surface (PES). Good agreement between experiment and theory is found, which confirms the accuracy of the CO-N potential energy surface for the 1460 cm collision energy studied by experiment. Experimental results for CO + N are compared with those for CO + CO collisions. The angle-resolved product rotational angular momentum alignment moments for the two scattering systems are very similar, which indicates that the collision induced alignment dynamics observed for both systems are dominated by a hard-shell nature. However, compared to the CO + CO measurements, the primary rainbow maximum in the DCSs for CO + N is peaked consistently at more backward scattering angles and the secondary maximum becomes much less obvious, implying that the CO-N PES is less anisotropic. In addition, a forward scattering component with high rotational excitation seen for CO + CO does not appear for CO-N in the experiment and is not predicted by QCT theory. Some of these differences in collision dynamics behaviour can be predicted by a comparison between the properties of the PESs for the two systems. More specific behaviour is also predicted from analysis of the dependence on the relative collision geometry of CO + N trajectories compared to CO + CO trajectories, which shows the special 'do-si-do' pathway invoked for CO + CO is not effective for CO + N collisions.