Collisions make chemical reactions possible. Scattering collisions kick reactants into excited states; reactive collisions finish the job. Understanding these collisions—being able to predict and control them—is one of physical chemistry’s ultimate prizes. With it would come not just the satisfaction of explaining chemical reactions from quantum fundamentals, but also the ability to steer such industrially important reactions as combustion.
The quest is daunting. Molecules, even simple ones, possess a plethora of quantum states, whose interactions with each other and with those of approaching reactants can create a mixture of thousands of initial and final states. Faced with this quantum stew, physical chemists who study collisions reduce the number of complicating ingredients by working with molecular beams. In this approach, the number of states is pared down to a handful, offering the theorist the hope of predicting what’s going on.
Two recent papers have applied molecular beams to probe a simple...
