23
Optical Spectroscopy and
Photochemistry
PRINCIPAL FACTS AND IDEAS
- Spectroscopy is the study of the interactions of matter with
electromagnetic radiation and the extraction of information about
molecular structure from this study.
- Emission and absorption of photons are governed by the Bohr frequency
rule:
Ephotonhν
hc
λ
Eupper−Elower
where theE’s are energy eigenvalues of two energy levels.
- Selection rules predict which transitions between pairs of levels will
occur with absorption or emission of radiation.
- Concentrations can be determined spectroscopically using the
Beer–Lambert law.
- Transitions between electronic energy levels produce spectra that are
generally in the visible and ultraviolet regions.
- Transitions between rotational states of molecules produce spectra in the
microwave region.
- Transitions between vibrational states of molecules produce spectra in the
infrared region.
- Photochemistry is closely related to spectroscopy and involves chemical
reactions that are initiated by absorption of radiation.
- Other types of optical spectroscopy such as Raman spectroscopy can
supplement emission/absorption spectroscopy.
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