光谱学Spectroscopy

物质只能吸收或发射能量恰好等于两能级之差 ΔE = hν 的光子。按波段和跃迁类型：γ 射线（核能级，穆斯堡尔谱）、X 射线（内层电子，XRF、XPS）、紫外-可见（价电子，UV-Vis）、红外（分子振动，IR、拉曼）、微波（分子转动，电子顺磁共振）和射频（核自旋，NMR）。按作用方式分为吸收光谱、发射光谱、散射光谱；按对象分为原子光谱（线状）和分子光谱（带状）。

Matter absorbs or emits only photons whose energy equals a gap between levels, ΔE = hν. By region and transition: γ-rays probe nuclear levels (Mössbauer), X-rays core electrons (XRF, XPS), UV–visible light valence electrons (UV-Vis), infrared molecular vibrations (IR, Raman), microwaves rotations and electron spins (EPR) and radio waves nuclear spins (NMR). By interaction there are absorption, emission and scattering spectra, and by object atomic spectra (lines) and molecular spectra (bands).

1666 年牛顿用棱镜把阳光分解成七色光谱。1802 年沃拉斯顿、1814 年夫琅禾费观察到太阳光谱中的暗线。1859–1860 年基尔霍夫和本生发现每种元素都有特征谱线，建立了光谱分析，并由此发现铯、铷，后来又发现铊、铟、氦（1868 年在太阳光谱中发现）。光谱学的研究直接推动了玻尔原子模型和量子力学的建立。

In 1666 Newton split sunlight into a spectrum with a prism. Wollaston (1802) and Fraunhofer (1814) saw dark lines in the solar spectrum. In 1859–60 Kirchhoff and Bunsen found that every element has characteristic lines, founded spectral analysis and discovered caesium and rubidium; thallium, indium and helium (found in the solar spectrum in 1868) followed. Spectroscopy drove the Bohr model and quantum mechanics.

光谱学是现代化学结构鉴定和定量分析的支柱：NMR、IR、UV、MS 合称“四大谱”用于有机结构解析；原子光谱用于元素分析；天文学通过光谱测定恒星成分、温度和运动速度；遥感光谱监测大气和地表；拉曼光谱用于文物、宝石和药品无损鉴定；医学中的磁共振成像和近红外脑功能成像也源于光谱学。

Spectroscopy is a pillar of modern structural and quantitative chemistry: NMR, IR, UV and MS, the 'four great spectra', solve organic structures; atomic spectroscopy analyses elements; astronomers read stars' composition, temperature and motion from spectra; remote sensing monitors the atmosphere and land; Raman identifies artworks, gems and drugs non-destructively; and medical MRI and near-infrared brain imaging also descend from spectroscopy.