Lecture 16. Vibrational Spectroscopy for Diatomic Molecules

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Lecture 16. Vibrational Spectroscopy for Diatomic
Molecules
References

• Engel, Ch. 8
• Molecular Quantum Mechanics, Atkins Friedman
  (4th ed. 2005), Ch.10
• A Brief Review of Elementary Quantum Chemistry
• http//vergil.chemistry.gatech.edu/notes/quantrev
  /quantrev.html
• Wikipedia (http//en.wikipedia.org) Search for
• Spectroscopy
• Infrared spectroscopy
• Raman spectroscopy
• Greenhouse effect

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and Transition Rate
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Selection Rules
To show a vibrational spectrum, a diatomic
molecule must have a dipole moment that varies
with extension.
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Selection Rules in
Transition probability ? 0 only if
Transition dipole moment ? 0, i.e.
? 0 only if
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Overtone, Second harmonics
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Greenhouse Gases and Global Warming
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N2 78.1 O2 20.9 H2O 0-2 Ar (inert gases)
0.936 CO2 370 ppm CH4 1.7 ppm N2O 0.35
ppm O3 10-8 ppm other trace gases
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CO2
v3 4.3 µm
v2 15 µm
v1 7.5 µm (IR inactive)
v3
v2
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H2O
O
o
H
H
bend v2 6.25 µm
symmetric stretch v1 2.74 µm
asymmetric stretch v3 2.66 µm
v3
v1
v2
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