Interaction of particles with each other often does not occur in a classical manner. As an example, one can think of collisions of heavy particles (atoms and molecules) with electrons and interaction with the light (photons). A quantum approach that is not based on the classical equations of motion is required to adequately capture the macroscopic properties of such matter. However, we encounter situations when the classical approach fails also for heavy particles.
Recent investigations of O2-Ar collisions reveal that vibrational deactivation is not properly captured by solving only classical equations of motions (think of upgraded second Newton Law). We have solved Schrodinger equations to discover that the discrepancies are observed at temperatures as low as 3000K – in a hypersonic regime!