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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Infrared (IR)

Light with wavelengths from about 750 nm to 1 mm, just longer than red. IR photons are too weak to excite most valence electrons but make molecules vibrate, which is why we feel IR as heat.

The electromagnetic spectrumFrom left to right: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, radio waves. Wavelength increases to the right; frequency and photon energy increase to the left. Visible light spans about 400 nm (violet) to 700 nm (red).γ-rayX-rayUVIRmicrowaveradio400 nmvisible700 nmlonger wavelength →← higher frequency and photon energy

Example

Hydrogen's Paschen lines (ending on n=3n = 3), such as 1875 nm for 4→34 \to 3, are all in the infrared.

See alsoElectromagnetic spectrumVisible lightPaschen series