Knowledge Bank

Special techniques are presented in the use of a high-frequency electrodeless discharge to produce emission spectra of some stable polyatomic molecules. The method utilizes the fact that the average energy in such a discharge depends directly upon the ionization potential of the gas and inversely on the pressure at which the discharge is maintained. By adjusting the energy conditions to a minimum and using a very rapid flow system, it is possible to produce rather high-intensity emission free from the overlying spectra of dissociation fragments. In the instances where the substance itself has a low vapor pressure or a relatively high ionization potential, the discharge may be maintained with some other material having the desired properties. Benzene, for example, was found useful for this purpose above 3200A. Because the intensity is greatly increased over that of fluorescence, the spectra can be studied conveniently at high dispersion with fairly narrow slit widths. The advantages of the technique made it possible to detect new features in some previously known spectra, and a new band system was found in the case of acetaldehyde.