1. H2, He2, and HeH
Step 1: A basis for H2: A B A B

2. H2, He2, and HeH (continued)
Step 2: Write down the Roothaan-equation

3. H2, He2, and HeH (continued)
reflection: A B s

4. H2, He2, and HeH (continued)
Step 3: Solve the Roothaan-equation A B A B

5. H2, He2, and HeH (continued)
Step 3: Solve the Roothaan-equation A B A B A B

6. H2, He2, and HeH (continued)

7. H2, He2, and HeH (continued)
energy of electron in lower MO
energy of electron in 1sH
bond energy:
(H2 is stable.)
neglect of overlap:

8. H2, He2, and HeH (continued)
Intermezzo: MO-diagrams and energy-levels
central column of
an MO-diagram
(MO-energy)
energy of the
whole system
(total energy)

9. H2, He2, and HeH (continued)

10. H2, He2, and HeH (continued)

11. H2, He2, and HeH (continued)
energy of electron in lower MO
energy of electron in upper MO
bond energy:
energy of electron in 1sHe
(He2 is not stable.)
Overlap should not be neglected here.

12. H2, He2, and HeH (continued)

13. H2, He2, and HeH (continued)
small overlap:

14. H2, He2, and HeH (continued)
He level shifted downwards
H level shifted upwards
ordering:
The average of the
levels increases.

15. H2, He2, and HeH (continued)
The lower MO resembles the 1s orbital of He.
The upper MO resembles the 1s orbital of H.

16. H2, He2, and HeH (continued)