infrared

Region of the electromagnetic spectrum extending from $780 nm$ to about $20 000 nm$ .

According to the CIE, the range between $780 nm$ and $1 mm$ is subdivided into:

IR-A $780$ – $1400 nm$

IR-B $1.4$ – $3 µm$

IR-C $3 µm$ – $1 mm$

Note:

This is the wavelength region in which absorption by a molecular entity causes excitation of its vibrational, rotational, and bending modes.

Source:

PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 354