Molecular velocities have been measured inside a hypersonic, normal shock wave, where the gas experiences rapid changes in its macroscopic properties. As first hypothesized by Mott-Smith, but never directly observed, the molecular velocity distribution exhibits a qualitatively bimodal character that is derived from the distribution functions on either side of the shock. Quantitatively correct forms of the molecular velocity distribution function in highly nonequilibrium flows can be calculated, by means of the Direct Simulation Monte Carlo technique.

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Several ionization and dissociation channels of electron interaction with the methane molecule are studied using the recently discovered robust scaling law [D. A. Erwin and J. A. Kunc, Phys. Rev. A 72, 052719 (2005)], other experimentally observed relationships between the ionization and dissociation channels, and the most recent information about the processes. The resulting cross sections for the channels are given in the form of analytical expressions valid at all nonrelativistic energies.

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Numerical experiments have been performed on normal shock waves with Monte Carlo Direct Simulations (MCDS's) to investigate the validity of continuum theories at very low Mach numbers. Results from the Navier—Stokes and the Burnett equations are compared to MCDS's for both hard-sphere and Maxwell gases. It is found that the maximum-slope shock thicknesses are described equally well (within the MCDS computational scatter) by either of the continuum formulations for Mach numbers smaller than about 1.2. For Mach numbers greater than 1.2, the Burnett predictions are more accurate than the Navier—Stokes results. Temperature—density profile separations are best described by the Burnett equations for Mach numbers greater than about 1.3. At lower Mach numbers the MCDS scatter is too great to differentiate between the two continuum theories. For all Mach numbers above one, the shock shapes are more accurately described by the Burnett equations.