Interferometric measurements in the spectrum of Ge I by Kaufman and Andrew show differences in wavelengths for 4<i>p</i>5<i>s</i>-4<i>p</i>6<i>p</i> lines emitted from different electrodeless discharge tubes containing germanium compounds and inert gases. The pattern of the shifts suggests that Stark effect is involved. This is illustrated on the basis of the theory for weak-field Stark effect for multiplets. The 6<i>p</i> level most sensitive to Stark effect is 6<i>p</i><sup>3</sup><i>P</i><sub>0</sub>. Through interaction with 5<i>d</i><sup>3</sup><i>D</i><sub>1</sub>, a field strength of 1.5 kV/cm shifts 6<i>p</i><sup>3</sup><i>P</i><sub>0</sub> by 0.01 cm<sup>-1</sup>.
LENNART MINNHAGEN, "Correlation between Observed Wavelength Shifts Produced in Electrodeless Discharge Tubes and Predicted Stark-Effect Shifts in the Spectrum of Neutral Germanium (Ge I)," J. Opt. Soc. Am. 54, 320-321 (1964)