电磁波谱Electromagnetic spectrum

无线电波（> 1 m）：核自旋跃迁，NMR；微波（1 mm–1 m）：分子转动、电子自旋，转动光谱、EPR、微波炉加热水分子；红外（780 nm–1 mm）：分子振动，红外光谱；可见光（约 380–780 nm）：价电子跃迁，颜色；紫外（10–380 nm）：价电子跃迁和光化学反应，UV 光谱、光电子能谱；X 射线（0.01–10 nm）：内层电子跃迁和晶体衍射；γ 射线（< 0.01 nm）：核能级跃迁。能量 E = hc/λ，波长越短能量越高：可见光光子约 1.6–3.3 eV，足以引起电子跃迁，但只有紫外以上才能断开大多数化学键。

Radio waves (longer than 1 m) drive nuclear-spin transitions in NMR; microwaves (1 mm–1 m) drive rotations and electron spins in rotational spectroscopy and EPR, and heat water in microwave ovens; infrared (780 nm–1 mm) excites vibrations in IR spectroscopy; visible light (about 380–780 nm) excites valence electrons and gives colour; ultraviolet (10–380 nm) drives valence transitions and photochemistry in UV and photoelectron spectroscopy; X-rays (0.01–10 nm) excite core electrons and are diffracted by crystals; and γ-rays (shorter than 0.01 nm) involve nuclear levels. Energy E = hc/λ rises as wavelength falls: visible photons carry about 1.6–3.3 eV, enough to excite electrons, but only UV and beyond break most bonds.

1800 年赫歇尔用温度计在可见光谱红端之外发现红外线；1801 年里特用氯化银变黑在紫端之外发现紫外线。1865 年麦克斯韦预言光是电磁波，1887 年赫兹用实验产生并检测到无线电波。1895 年伦琴发现 X 射线，1900 年维拉德发现 γ 射线，从此电磁波谱的全貌被认识。

In 1800 Herschel found infrared beyond the red end of the spectrum with a thermometer, and in 1801 Ritter found ultraviolet beyond the violet end by the darkening of silver chloride. Maxwell predicted in 1865 that light is an electromagnetic wave, and Hertz produced and detected radio waves in 1887. Röntgen discovered X-rays in 1895 and Villard gamma rays in 1900, completing the picture.

不同波段广泛用于通信（无线电、微波）、加热与雷达（微波）、热成像和遥控（红外）、照明与光合作用（可见光）、杀菌消毒和光刻（紫外，深紫外 193 nm 和极紫外 13.5 nm 用于芯片制造）、医学成像和晶体学（X 射线）以及放射治疗和灭菌（γ 射线）。

Its regions serve communication (radio, microwaves), heating and radar (microwaves), thermal imaging and remote controls (infrared), lighting and photosynthesis (visible), disinfection and lithography (UV; deep-UV 193 nm and extreme-UV 13.5 nm light make chips), medical imaging and crystallography (X-rays), and radiotherapy and sterilisation (γ-rays).