General Aspects of Molecular Spectroscopy

The Born-Oppenheimer approximation (see Section 6.1) treats the motion of electrons and nuclei on very different time scales. The electrons, being much less massive, move much more rapidly than the nuclei in a molecule. In the Born-Oppenheimer approximation, we consider the nuclei to be frozen at particular locations and calculate the electronic energy levels and wave functions (molecular orbitals) for the rapidly moving electrons (see Chapter 6). We find that the allowed 

Spectrai Region Frequency (s ) Energy Leveis Invoived Information Obtained 

Radio waves 10 -10 Nuclear spin states Electronic structure near the nucleus 

Microwave, far infrared 10 -10 Rotational Bond lengths and bond angles 

Visible, ultraviolet Valence electrons Electron configuration 

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