Far infrared rays - Ensekigaisen

Within the infrared range, which has wavelengths between 0.8 μm and 1 mm, electromagnetic waves with wavelengths of 2.5 μm or longer are called far-infrared rays. They can also be divided into near-infrared (0.8-2.5 μm), mid-infrared (2.5-25 μm), and far-infrared (25 μm-1 mm), but there are no clear boundaries. Many rotational spectra of molecules with dipole moments fall into the far-infrared range.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

波長が0.8 μm～1 mm の赤外領域のうち，2.5 μm 以上の長波長の電磁波を遠赤外線という．近赤外(0.8～2.5 μm)， 中赤外(2.5～25 μm)，遠赤外(25 μm～1 mm)という分け方もあるが，明確な境界があるわけではない．双極子モーメントをもつ分子の回転スペクトルの多くが遠赤外領域に入る．

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