Imaging rotational energy transfer: comparative stereodynamics in CO + N2 and CO + CO inelastic scattering

State-to-state rotational energy transfer in collisions of ground ro-vibrational state (CO)-C-13 molecules with N-2 molecules has been studied using the crossed molecular beam method under kinematically equivalent conditions used for (CO)-C-13 + CO rotationally inelastic scattering described in a previously published report (Sun et al., Science, 2020, 369, 307-309). The collisionally excited (CO)-C-13 molecule products are detected by the same (1 + 1 & PRIME; + 1 & PRIME;& PRIME;) 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)-C-13 + N-2 scattering images and compare them with theoretical predictions from quasi-classical trajectories (QCT) on a newly calculated (CO)-C-13-N-2 potential energy surface (PES). Good agreement between experiment and theory is found, which confirms the accuracy of the (CO)-C-13-N-2 potential energy surface for the 1460 cm(-1) collision energy studied by experiment. Experimental results for (CO)-C-13 + N-2 are compared with those for (CO)-C-13 + 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)-C-13 + CO measurements, the primary rainbow maximum in the DCSs for (CO)-C-13 + N-2 is peaked consistently at more backward scattering angles and the secondary maximum becomes much less obvious, implying that the (CO)-C-13-N-2 PES is less anisotropic. In addition, a forward scattering component with high rotational excitation seen for (CO)-C-13 + CO does not appear for (CO)-C-13-N-2 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)-C-13 + N-2 trajectories compared to (CO)-C-13 + CO trajectories, which shows the special 'do-si-do' pathway invoked for (CO)-C-13 + CO is not effective for (CO)-C-13 + N-2 collisions.

Automated summary

This study investigates state-to-state rotational energy transfer in collisions between (CO)-C-13 molecules and N-2 molecules. The experimental results agree well with theoretical predictions, confirming the accuracy of the experiment. The collision dynamics behavior in (CO)-C-13 + N-2 collisions differs from that in (CO)-C-13 + CO collisions.