![]() This has a diffuse series as well with wavelengths at 6678, 49 Å. Helium when ionised is termed He II and has a spectrum very similar to hydrogen but shifted to shorter wavelengths. Helium has a diffuse series of doublet lines with wavelengths 5876, 44 Å. Helium is in the same category as alkaline earths with respect to spectroscopy, as it has two electrons in the S subshell as do the other alkaline earths. The diffuse series of singlet lines has series letter S and formula 1P-mS. Potassium potassium diffuse series Ī diffuse series of triplet lines is designated by series letter d and formula 1p-md. When n tends to infinity the diffuse and sharp series end up with the same limit. In alkali metals the P terms are split 2 P 3 2 The limit for the series corresponds to electron emission, where the electron has so much energy it escapes the atom. The Rydberg correction is largest for the S term as the electron penetrates the inner core of electrons more. Since the Electron in the D subshell state is not the lowest energy level for the alkali atom (the S is) the diffuse series will not show up as absorption in a cool gas, however it shows up as emission lines. The terms can have different designations, mD for single line systems, mδ for doublets and md for triplets. One terminology to identify the lines is: 1P-mD But note that 1P just means the lowest P state in the valence shell of an atom and that the modern designation would start at 2P, and is larger for higher atomic numbered atoms. The series is caused by transitions from the lowest P state to higher energy D orbitals. ![]() The diffuse series is due to the 3p-nd transitions shown here in blue.
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