Question

Suppose you have a friend who is a sophomore majoring in physics. Explain the concept of spin correlation to her (this is is physical chemistry question relating to singlet and triplet states of complex atoms, specifically how the energy of a triplet is larger than that of its singlet counterpart, if I'm not mistaken)

Answer 1

for suppose if we have two electrons in the ground state then both electrons are paired up and the total spin will result zero. basically, electrons do have spin due to its intrinsic angular momentum caused in them. electron spin has a value of 1/2 it can be either +1/2 (clockwise spin) or -1/2(anti-clockwise spin). mainly singlet and triplet states are arised in photochemistry they can be shown as below

we can observe that in the ground state the electrons are paired up in the excited singlet state due to the applied magnetic field the orientation of electron changes due to this one of the electron gets excited from ground state to excited state. In this case, the pairing of electrons remains same. in another case in the excited triplet state, the electrons are not paired.

the number of excited states can be derived by using spin multiplicity rule that is 2S+1 where S is a summation of all spins of individual electrons.

in the case of excited singlet state spin multiplicity is 2[+1/2+(-1/2)]+1 = 2[0] +1 = 1

in the case of excited singlet state spin multiplicity is 2[+1/2+(+1/2)]+1 = 2[1] +1 = 3

the three excited states are shown as below.

triplet state will be having a long life so it posses high energy compared to that of singlet excited state.