Widths and Profiles of Spectral Lines
Spectral lines in discrete absorption or emission spectra are never strictly monochromatic. Even with the very high resolution of interferometers one observes a spectral distribution I(v) of the absorbed or emitted intensity around the central frequency v0 = (Ei - Ek)/h corresponding to a molecular transition with the energy difference ∆E = Ei - Ek between upper and lower level. The function I(v) in the vicinity of v0 is called the line profile (see Fig.3.1). The frequency interval δv = ∣v2 - v1∣ between the two frequencies vl and v2 for which I(v1) = I(v2) = I(v0)/2 is the full width at half maximum of the line (FWHM), often shortly called the linewidth or half— width of the spectral line.
KeywordsLine Profile Inelastic Collision Elastic Collision Line Shift Doppler Width
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