source; VG scienta VUV5000 manual
Total angular momentum L=Σlj L=0-> S, L=1-> P, L=2->D...
Total angular spin momentum S=Σsj , Multiplicity 2S+1
Meaning of 2p 1P:
The first "2p" means that an electron in He atom is in 2p ( excited).
1 at the left upper shoulder of P means that the multiplicity of the total angular spin momentum is 1.
P means that the Total angular momentum L =1.
This situation is achieved when an electron is in the 2p orbital having the spin angular momentum of 1/2, and the other electron is in the 1s orbital having the spin angular momentum of 1/2. This situation gives that the total angular momentum L=Σlj = 0+1 = 1, and the total angular spin momentum S=Σsj = 1/2 - 1/2 =0 and the multiplicity = 2*0 + 1 = 1.
Energy difference of He I α and He II α = 40.814-21.2182 = 19.5958 eV.
When the Fermi energy is at the electron kinetic energy of 16.95eV in the experiment with He I α,
the Fermi energy with He IIα is at the kinetic energy of 16.95 +19.5958 = 36.5458 eV.