[UPSC CSE 2001] Atomic Physics (Q114, (12+6+12)M)

(i) On the basis of vector atom model, discuss briefly the L-S and J-J coupling schemes. (ii) Write down expressions for spin angular momentum, orbital angular momentum and total angular momentum under L-S coupling scheme. (iii) Obtain the energy states for ^{2}\text{He} atom for n = 1, 2, 3 levels (n is principal quantum number). Draw the energy level diagram. Does L-S coupling scheme hold good in ^{80}\text{Hg} atom which like He has 2 optical electrons (6S^2) ? Comment.