Chemico-physical processes in shock waves

This article describes the application of shock waves to the study of various processes of chemico-physical interest during the past five to ten years. It is mainly concerned with those processes of atomic and molecular physics which derive from the thermal transfer of energy in the temperature range 1000 to 10 000 °K. These include the following: the excitation of rotational and vibrational energies in molecules; the dissociation of simple diatomic molecules, including restrictions which may be imposed on the rate for this and the converse process of recombination owing to non-Boltzmannian energy distributions within the molecule; relaxation processes in nozzle-expansion flows; the ionization of atoms and simple molecules, including such processes as autoionization and the effective lowering of the ionization potential owing to the depression of continuum states; and spectroscopic measurements of oscillator strengths, or f values, for electronic transitions in atoms and refractory elements, including mention of the processes by which such transitions are excited. A final section considers some topical aspects of shock waves, such as their use in the production of intense molecular beams and their suggested use to promote population inversions, and hence laser action, in suitable gases. These discussions are preceded by an account of the physical nature and properties of shock waves, and of the methods used for their controlled production in laboratories. A brief description is given of the instrumentation used in shocktube work, and an essential review of the limitations imposed on shock-tube flows by gas-dynamic influences is included.