# Who associated the sharp, principal, diffuse, fundamental spectral terms with electron's momentum?

It is well documented that the notation for the electronic configuration (s,p,d,f) of atoms as used today originates from the words sharp, principal, diffuse, fundamental from alkali metal spectra (William B Jensen has written a nice article here). After searching for a while

1. I never got a chance to find the entire alkali metal spectra where we can visually show the students that this set of lines was called sharp, this set of lines is called the principal, and this is the fundamental set. Does anyone recall a photograph of a real spectrum of any alkali metal with the series labeled in any reference or text (not all the lines are in the visible)? Are there any photographic plates which label all the four series?

2. Who was the first person to associate the descriptors of spectral lines with angular momentum values of l = 0 implies s, l=1 implies p, l=2 is d and so on? If we look at Hund's open preview of Linienspektren "https://www.amazon.com/Linienspektren-Periodisches-Elemente-Eigenschaften-Einzeldarstellungen/dp/3642495400" pg 3, he uses the s,p,d and calls them Rydberg correction. How come they got associated with angular momentum?

Thank you.

Yes, those terms come from spectroscopy; they refer to the appearance of the spectral lines.

It wasn't until quantum mechanics that atomic spectra were understood as an effect of electron energy levels, including electron angular momentum.

From Linus Pauling's concise in his Introduction to Quantum Mechanics ch. 5 ("The Hydrogen Atom"):

The hydrogen atom has held a prominent place in the development of physical theory. The first spectral series expressed by a simple formula was the Balmer series of hydrogen. Bohr's treatment of the hydrogen atom marked the beginning of the old quantum theory of atomic structure, and wave mechanics had its inception in Schrödinger's first paper, in which he gave the solution of the wave equation for the hydrogen atom. Only in Heisenberg's quantum mechanics was there extensive development of the theory (by Heisenberg, Born, and Jordan) before the treatment of the hydrogen atom, characterized by its difficulty, was finally given by Pauli. In later developments,* beyond the scope of this book, the hydrogen atom retains its important position; Dirac's relativistic quantum theory of the electron is applicable only to one-electron systems, its extension to more complicated systems not yet having been made.

*Even finer energy levels were later discovered by Willis Lamb of "Lamb shift" fame.

Schrödinger was the first who "gave the solution of the wave equation for the hydrogen atom". In solving the differential equation, he had to introduce integer constants called the

1. total quantum number ($$n=1,2,3,…$$)

2. azimuthal quantum number ($$\ell=0,1,2,…,n-1$$)

3. magnetic quantum number ($$m=-\ell,-\ell+1,…,0,\ell-1,\ell$$).

However, these quantum numbers did have analogues in the older quantum theory of Bohr, Sommerfeld, et al.

• Thanks. As per Jensen's article, Bohr did not use the s,p,d,f notation. Who was the first person to associate the descriptors of spectral lines with angular momentum values of l = 0 implies s, l=1 implies p, l=2 is d and so on? It seems like it must be Hund but his book on Linienspektren is not translated. My German is not good enough to figure out the finer details. However, his book does use s,p,d,f notation for configuration. I am not sure if he was the first one to associate spdf with angular momentum values of 0,1,2,3 – M. Farooq Jan 24 '19 at 21:52