Sharp series

The sharp series is a series of spectral lines in the atomic emission spectrum caused when electrons descend from higher-energy s orbitals of an atom to the lowest available p orbital. The spectral lines include some in the visible light, and they extend into the ultraviolet. The lines get closer and closer together as the frequency increases never exceeding the series limit. The sharp series was important in the development of the understanding of electron shells and subshells in atoms. The sharp series has given the letter s to the s atomic orbital or subshell.

The sharp series has a limit given by

${\displaystyle v={\frac {R}{\left[2+p\right]^{2}}}-{\frac {R}{\left[m+s\right]^{2}}}{\text{ with }}m=2,3,4,5,6,...}$

The series is caused by transitions to the lowest P state from higher energy S orbitals. One terminology to identify the lines is: 1P-mS^[1] But note that 1P just means the lowest P state in an atom and that the modern designation would start at 2P, and is larger for higher atomic numbered atoms.

The terms can have different designations, mS for single line systems, mσ for doublets and ms for triplets.^[2]

Since the P state is not the lowest energy level for the alkali atom (the S is) the sharp series will not show up as absorption in a cool gas, however it shows up as emission lines. The Rydberg correction is largest for the S term as the electron penetrates the inner core of electrons more.

The limit for the series corresponds to electron emission, where the electron has so much energy it escapes the atom. Even though the series is called sharp, the lines may not be sharp.^[3]

In alkali metals the P terms are split ${\displaystyle 2P_{\frac {3}{2}}}$ and ${\displaystyle 2P_{\frac {1}{2}}}$. This causes the spectral lines to be doublets, with a constant spacing between the two parts of the double line.

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