“…With the additional knowledge of the isotope shifts and the hyperfine structure splitting of the used transition a correction for the overlap can be performed. References for isotope shift and hyperfine structure data are given, e.g., by Heilig [27][28][29][30] and Fuller [31]. The Doppler width, Δν D , is obtained by Here, λ is the transition wavelength, k is Boltzmann's constant, T is the temperature in K and M is the mass of the atoms or molecules.…”