# Notation in atomic structure

In the book, The theory of atomic structure and spectra, Robert D. Cowan says that the allowed terms of $$p^2$$ are $$^1S$$, $$^1D$$, $$^3P$$ and so the possible terms of $$p^2 + p\quad$$ (obtained by using the vector model) are:

$$^2P^\circ,\quad ^2P^\circ D^\circ F^\circ,\quad ^{2,4}S^\circ P^\circ D^\circ \tag1$$

I am having trouble in understand the notation in $$(1)$$. For example the term $$^2P^\circ$$ means that $$s=1/2,l=1$$ and $$^\circ$$ means odd parity, but for the term $$^{2,4}S^\circ P^\circ D^\circ$$, I do not know what it means. Can anyone explain me it please?

• My guess is that $\quad ^{2,4}S^\circ P^\circ D^\circ$ means $^2S^\circ, ^2P^\circ,^2D^\circ,^4S^\circ, ^4P^\circ,^4D^\circ$ Apr 28 '20 at 21:25

This illustrates the notion that $$p^2$$ and $$p^4$$ are equivalent.
I think the 2,4 superscript in Cowan's book for $$^{2,4}S^\circ P^\circ D^\circ$$ is a peculiar notation of his. Most other books seem to presume the reader knows the equivalency.