A Method of Determining Optical Cross Sections*†

A method of evaluation of the optical cross sections, i.e., cross sections for broadening collisions between excited atoms and foreign molecules, from experimental intensity-density data is described. This method utilizes the analytical expressions of the asymptotes to the theoretical intensity-density curves at very low, and at very high densities of the emitting atoms. Only relative intensity measurements are necessary for the evaluation of the cross sections. An intensity-density graph for the Na5890 line is constructed from photoelectric measurements of the total line intensities, emitted from a Lundegårdh-type acetylene-air flame. The optical cross section for sodium corresponding to this line is found to be 64 square angstroms. A brief discussion of the possibilities of utilizing this method for the determination of the degrees of dissociation of metal salts in the flame, or the evaluation of absolute and relative f values of the spectral lines is included at the end of the paper.