Home work Physical and Theoretical Chemistry IV

- Molecular Spectroscopy -

Discussion  Wed 22.5.2002 at 10:30,  HR30.1 (Hagenring 30)



 

Home work 4            MOs
 

In the following use this energetic order:

g < 1σu < 2σg < 2σu < 1πu < 3σg < 1πg < u< 4σg< 4σu< 2πu< 5σg< 2πg< 5σu
 
 

Exercise 1: Dissociation energies

Why is the dissociation energy of N2 larger than that of N2+, while the dissociation energy of O2 is smaller than that of O2+?
Use the bond strengths for this discussion. The bond strength is given by (B - A)/2, where
B is the number of electrons in the bonding orbital and
A is the number of electrons in the antibonding orbital
 
Exercise 2:   -  B2
The ground state configuration of B2 is given by 1σg2u2g2u2u2
a) What terms for the total electron configuration are possible?
b) Promote one electron from the 1πu MO to the 3σg MO. Which terms are now possible?
c) Which transitions between all possible terms are allowed?
 
Exercise 3:  heteronuclear molecules
Calculate the (exact) energies of the bonding and of the antibonding s molecular orbitals of LiH. Assume that only the  Li-2s atomic orbital and the H-1s atomic orbital form that s MO  (i.e. forget about the 2p orbitals).
Solve the equation (αLi - E) · (αH - E) - (β - E·S)2 = 0, but use the given values of αLi, αH, b, and S (in advance):
αLi = -0,23        αH = -0,39        β = -0,21          S = 0,47