Chappuis Bands
Definition and meaning of Chappuis Bands in chemistry.
Chappuis bands are the weak, broad absorption bands of ozone (O3) in the visible region of the electromagnetic spectrum, spanning roughly 400 to 650 nm with a maximum near 600 nm. They are the only significant ozone absorption feature in visible light.
In more detail
This absorption comes from an electronic transition in the ozone molecule that is intrinsically much weaker than the strong ultraviolet Hartley and Huggins bands, so it gives concentrated ozone only a faint blue tint rather than the intense UV blocking those bands provide. Because ozone absorbs so little visible light elsewhere, the Chappuis band is the practical spectral window used to retrieve ozone concentrations from ground-based and satellite instruments working outside the UV. It was first characterized by the French chemist James Chappuis in 1880.
Key facts
| Formula | O3 (ozone) |
|---|---|
| Wavelength range | ~400-650 nm, peak near 600 nm |
| Discoverer | James Chappuis (1880) |
| Field | Physical Chemistry |
Differential optical absorption spectroscopy (DOAS) instruments measure light attenuation across roughly 450-590 nm to retrieve stratospheric total column ozone using the Chappuis band.
Frequently asked questions
How does the Chappuis band differ from the Hartley and Huggins bands?
The Hartley band (~200-310 nm) and Huggins band (~310-350 nm) are strong ultraviolet absorptions that account for most of ozone's UV shielding, while the Chappuis band is a much weaker, broader absorption in the visible range (~400-650 nm) peaking around 600 nm.
Why is the Chappuis band useful in atmospheric science?
Since it is the only notable ozone absorption in visible light, it lets ground-based and satellite spectrometers measure total column ozone using visible wavelengths, complementing UV-based retrieval methods.