Observation of correlated excitations in bimolecular collisions

• Published in: Nature chemistry 2018-04, Vol.10 (4), p.469-473
• Main Authors: Gao, Zhi, Karman, Tijs, Vogels, Sjoerd N., Besemer, Matthieu, van der Avoird, Ad, Groenenboom, Gerrit C., van de Meerakker, Sebastiaan Y. T.
• Format: Article
• Language: English
• Subjects: 639/638/440/94; 639/638/440/948; Analytical Chemistry; Biochemistry; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Collisions; Correlation; Energy gap; Excitation; Inorganic Chemistry; Nitric oxide; Organic Chemistry; Physical Chemistry; Potential energy; Radicals; Scattering cross sections; Velocity
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/s41557-018-0004-0

Although collisions between atoms and molecules are largely understood, collisions between two molecules have proven much harder to study. In both experiment and theory, our ability to determine quantum-state-resolved bimolecular cross-sections lags behind their atom–molecule counterparts by decades. For many bimolecular systems, even rules of thumb—much less intuitive understanding—of scattering cross sections are lacking. Here, we report the measurement of state-to-state differential cross sections on the collision of state-selected and velocity-controlled nitric oxide (NO) radicals and oxygen (O 2 ) molecules. Using velocity map imaging of the scattered NO radicals, the full product-pair correlations of rotational excitation that occurs in both collision partners from individual encounters are revealed. The correlated cross sections show surprisingly good agreement with quantum scattering calculations using ab initio NO−O 2 potential energy surfaces. The observations show that the well-known energy-gap law that governs atom–molecule collisions does not generally apply to bimolecular excitation processes, and reveal a propensity rule for the vector correlation of product angular momenta. Collisions between atoms and molecules are largely understood; however, our understanding of collisions between two molecules is lacking because they are significantly harder to study, Now, correlated rotational excitations have been observed in inelastic collisions between NO and O 2 molecules. It is shown that the energy-gap law that governs atom–molecule collisions does not generally apply to bimolecular excitation processes.