In the present chapter some prototype gas and gas-surface processes occurring within the hypersonic flow layer
surrounding spacecrafts at planetary entry are discussed. The discussion is based on microscopic dynamical calculations
of the detailed cross sections and rate coefficients performed using classical mechanics treatments for atoms, molecules
and surfaces. Such treatment allows the evaluation of the efficiency of thermal processes (both at equilibrium and non
equilibrium distributions) based on state-to-state and state specific calculations properly averaged over the population of
the initial states. The dependence of the efficiency of the considered processes on the initial partitioning of energy among
the various degrees of freedom is discussed.