The characteristic distribution of photon emission and absorption as a function of
although the approximations used to derive certain classes of lineshape (such as the van Vleck-weisskopf lineshape) preclude normalization. The simplest approximation used for emission at a frequency is simply the delta function, Eric Weisstein's World of Math
Ben-Reuven (1975) discussed the Liouville space Eric Weisstein's World of Math approach to spectral lineshape theory.
Ben-Reuven Lineshape, Doppler Lineshape, Kinetic Lineshape, Lorentzian Lineshape, Sub-Lorentzian Lineshape, van Vleck-Weisskopf Lineshape, Voigt Lineshape
References
Ben-Reuven, A. "Spectral Line Shapes in Gases in the Binary Collision Approximation." Advan. Chem. Phys., Vol. 33 (Ed. I. Prigogine and S. A. Rice). New York: Wiley, pp. 235-293, 1975.
Waters, J. W. "Absorption and Emission by Atmospheric Gases." Ch. 23 in Methods of Experimental Physics, Vol. 12B (Ed. M. L. Meeks). New York: Academic Press, p. 147, 1976.
