The Stark effect for mercury
The Stark effect in the mercury spectrum has already received some attention. The first observations were made by Wendt and Wetzel, who used a canal-ray method. They reported small displacements in the diffuse series groups 2 3 P i — n 3 D i , n = 4, 5, 6, and in the sharp series line 2 3 P 1 —4 3 S. Ritter investigated the effect, using a Lo Surdo source, and noted small displacements toward the red in the lines 2 3 P 0 —5 3 D 1 , 2 3 P 1 —6 3 D 2 in the fields up to 26,000 volts per centimetre. Using an absorption method, Terenin detected a definite effect in the diffuse series triplets 2 3 P i — 3 3 D i . A far more extensive and valuable investigation of the effect for mercury was made by Hansen, Takamine and Werner at the Institute for Theoretical Physics, Copenhagen. A fine column of mercury in a quartz tube served as the cathode of a discharge tube. The light immediately above the mercury surface was analysed with a Hilger E 2 spectrograph. Observations were limited mainly to the diffuse series triplets 2 3 P i — n 3 D i , and the associated combination lines which appeared even in low electric fields. For values of n lower than five no definite Stark effect was observed, but in the higher members of the three series the 3 D lines were displaced to the red by an amount which increased with increasing term number. Grouped about the 3 D lines new combination lines of the types 3 P— 3 F, 3 P— 3 G, etc., were photographed and interpreted on the Bohr theory. In these mercury line groups, the restriction regarding the change in the azimuthal quantum number (∆ k = ± 1) is removed by low external fields, hence the new lines may be traced to a point very near their zero field position. No analysis of the patterns formed by individual lines could be attempted, however, since the electric fields which were established in the source were too weak to permit the necessary resolutions.
