1. Molecules
E&R Chapter 12

2. Outline Bonding 12-1 Molecular Excitations 12-4 Ionic 12-2
Covalent 12-3
Molecular Excitations 12-4
Rotation 12-5
Vibration 12-6
Electronic
Electronic + Vibration + Rotation 12-7

3. Bonding
R Nave, Georgia State Univ

4. Chemical Bonding
R Nave, Georgia State Univ

5. Ionic Bonds
RNave, GSU at

6. Ionic Bonds

7. Ionic Bonding
RNave, Georgia State Univ at hyperphysics.phy-astr.gsu.edu/hbase/molecule

8. Ionic Bonding
a.u. = atomic energy unit = 2*(13.6eV)
Brandsen&Joachim

9. E&R

10. Covalent Bonds
RNave, GSU at

11. Covalent Bonding
SYM ASYM
spatial spin
ASYM SYM
spatial spin

12. Covalent Bonding not really parallel, but spin-symmetric Stot = 1
not really anti, but spin-asym

13. Covalent Bonding
Bransden&Joachin

14. Ionic vs Covalent Bond Properties
Ionic Characteristics
Crystalline solids
High melting & boiling point
Conduct electricity when melted
Many soluble in water, but not in non-polar liquids
Covalent Characteristics
Gases, liquids, non-crystalline solids
Low melting & boiling point
Poor conductors in all phases
Many soluble in non-polar liquids but not water

15. Rotational Spectra w
rotational A.M.
moment of inertia

16. Rotation

17. Rotation

18. Rotational Spectra

19. Ocean Optics: Nitrogen N2
~ 0.3 eV
~ 0.4 eV

20. Vibration HF 970 HCl 480 HBr 410 Hi 320 CO 1860 NO 1530 “Spring Const”
Molecule
“Spring Const”
( N/m ) HF
970
HCl
480
HBr
410 Hi
320 CO
1860 NO
1530

21. Vibration (in an Electronic state)

22. Electronic + Vibration

23. Electronic + Vibration + Rotation
2.550 eV
2.656 eV
electronic excitation gap
vibrational excitation gaps

24. Electronic + Vibration + Rotation
Vibrational Well
Vibrational Well
2.656 eV
depth ~ eV
electronic excitation gap
vibrational excitation gaps

25. Electronic, Vibration, Rotation
Electronic ~ optical & UV
~ 1 – 3 eV
Vibration ~ IR
~ 10ths of eV
Rotation ~ microwave
~ 1000ths of eV

26. Electronic + Vibration + Rotation
2.550 eV
2.656 eV
electronic excitation gap
vibrational excitation gaps

27. ** + Vibration + Rotation
IN A DIATOMIC MOLECULE
because a photon has one unit of
angular momentum,
the rotational quantum number
must change
(vib is not angular motion)
Dr = 0 not allowed

28. ** + Vibration + Rotation

29. Ocean Optics: Nitrogen N2
~ 0.3 eV
~ 0.4 eV

31. Some Molecular Constants
Molecule
Equilibrium Distance
Ro (Å)
Dissociation NRG
Do (eV)
Vibrational freq
v a (cm-1)
Moment of Inertia
Bb (cm-1)
H2+
1.06
2.65
2297
29.8 H2
0.742
4.48
4395
60.8 O2
1.21
5.08
1580
1.45 N2
1.09
9.75
2360
2.01 CO
1.13
9.60
2170
1.93 NO
1.15
5.3
1904
1.70
HCl
1.28
4.43
2990
10.6
NaCl
2.36
4.22
365
0.190
Notes: a) vibrational frequency in table is given as f / c
b) moment of inertia in table is given as hbar2/(2I) / hc

32. Fluorescence
absorb at one wavelength,
emit at another

33. Phosphorescence
tunneling slows the decay process