Posmom: The unobserved observable

We have recently shown that the probability density S(s) of the position-momentum dot product s = rp of a particle can be computed efficiently from its wave function ψ(r). Here, by examining the H atom and LiH molecule, we show that S(s) yields insight into the nature of electronic trajectories, and we argue that electron posmometry provides information that is inaccessible by diffraction or momentum methods.