Absorption Spectra of Gaseous Species Formed at Flash-Heated Solid Surfaces

Abstract

A method is described for recording the absorption spectra of gaseous atoms and molecules produced at strongly heated solid surfaces. A very intense pulse of light from a capacitor discharge lamp falls on light-absorbing grids placed in the absorption path of a spectrograph. The diameter of the grid windings is sufficiently small that their temperatures rise several thousand degrees very rapidly. The gaseous thermal species that are formed in the optical path arise from the following reactions: (1) vaporization of the grid material; (2) vaporization of coatings applied to the grids; and (3) reactions of the grids with a surrounding gas. Flash spectroscopic recording is used. The following illustrations of the technique are presented: the formation of atomic tungsten by the vaporization of tungsten grids; the formation of AlCl by the evaporation of AlCl3 from carbon grids; and the formation of CH3, CD3, and CF2 by the reaction of heated carbon grids with CH4, CD4, and CF4, respectively. Flash heating compares favorably with flash photolysis as a way to produce labile species for kinetic absorption spectroscopy. Parent molecules need not absorb in the near ultraviolet since the dissociative processes that occur are thermal rather than photolytic. Container problems for high-temperature studies are virtually eliminated because of the pulse nature of the experiment.