Short-time single particle dynamics in quantum and molecular systems

Recent experimental and theoretical results on the short-time single particle dynamics of atomic and molecular systems are reviewed. Results on momentum distribution, n(p), and single particle mean kinetic energy, <Ek>, are presented, both in atomic (quantum) systems such as 3He and 4He in the normal and superfluid state, and in molecular systems such as H2, H2S and H2O. The main experimental technique employed for these measurements is known as deep inelastic neutron scattering, i.e. neutron scattering at high wavevector and energy transfers. This is the only experimental technique which allows the direct measurement of n(p) and <Ek>, interesting physical quantities in any systems where the short-time dynamic behavior departs from the classical one.