In general chemistry texts, the electron configurations are sometimes shown in boxes with up and down arrows to show the concept of paired spins. My impression for years was that Hund used such diagrams. However, flipping through his book Linienspektren und Periodisches System der Elemente which used the s,p, d, f notation in a modern way, there is no such use of box diagrams with up and down arrows. Does anyone know who introduced this so-called box notation? Thanks.
This image is from Atomic Spectra and Atomic Structure by Gerhard Herzberg, John William Tranter Spinks - 1944. It does not really have boxes (just boxes of a table), but spin +1/2 and spin -1/2 are shown as arrows. Of course, I am not claiming this is the first usage, just that in 1944 it existed.