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Width of the Spectral Line

— size frequency interval $\Delta \nu$, characterizing as monochromatic radiation of atoms, molecules and other quantum systems. Natural W.of the s.l. associated with finite duration single act atomic radiation $\left(\tau \sim 10^{-8} \mathrm{s}\right)$ and equal $\Delta \nu_{\mathrm{e c m}} \sim 10^{8} c^{-1}$. The impact of electric and magnetic fields and thermal motion of atoms and molecules at different speeds relative to the measuring device (see. Doppler effect) lead to increased spectral lines (see. also monochromatic radiation).