Intensities in the Stark Effect of Helium

Theory of the intensity of combination lines in the Stark effect.—The quantum theory of dispersion may be applied to the Stark effect in a weak field by considering the atoms exposed to external radiation of zero frequency. This makes it possible to calculate the intensity of new lines appearing in the field (combination lines) from the intensity of lines appearing in the undisturbed spectrum. The theory is applied here to the helium spectrum.

Measurements of the intensity of combination lines of He in the Stark effect.—Measurements of the intensity of the helium lines $2P-nM$, $2P-nm$, $2S-4M$, where $n=4, 5, 6, 7$; $M=P, D, F$, etc., are given. The Lo Surdo method of obtaining emission in an electric field was used, with the cathode set with its surface parallel to the slit of the spectrograph. A photographic method of measuring the intensities, using a Moll photometer to measure the photographic density was used. The intensity of the combination lines increases as the square or higher powers of the electric field, as the theory demands. The ratio of the intensity of the combination lines to the nearest lines in the spectrum emitted by the undisturbed atom is in approximate agreement with that calculated from the theory.