Data from: Molecular square dancing in CO-CO collisions

Collision between two carbon monoxide (CO) molecules at a collision energy of 1460 cm-1 has been investigated by measuring velocity-map ion images for rotationally excited CO molecules using a crossed molecular beam apparatus in combination with a VUV (Vacuum Ultra-Violet) REMPI (Resonance Enhanced Multi Photon Ionization) scheme. Partially resolved pair-correlated differential cross sections (PC-DCSs) were extracted for analysis of the radius-dependent angular distribution of the image using an onion-peeling inversion procedure. The experimental results of this analysis were compared with advanced theory, in particular with the predictions of QCT (Quasi-Classical Trajectory) calculations, and good agreement between experiment and theory was found. An extraordinary energy transfer channel is revealed, featuring forward scattering while both CO product molecules are highly rotationally excited, which defies prediction from prevailing models of inelastic scattering. An extraordinary energy transfer channel is revealed, featuring forward scattering while both CO product molecules are highly rotationally excited, which defies prediction from prevailing models of inelastic scattering. Simulation by quasi-classical trajectories on an accurate intermolecular potential energy surface and opacity function analysis show that these unusual product events start with the large C ends of CO colliding with each other, with immediate and large transfer from translational to rotational energy. This forward-scattered-symmetric-excitation behaviour was also cinfirmed by Quantum Close-Coupling calculations.