The occurrence of non-Gaussian spectral lines shapes of molecules in electrostatically disordered media

We calculate the effects of relatively strong electric fields, corresponding to typical values for the fields inside glasses and proteins, on the spectroscopic properties of a simple two-level molecule. Disorder in the electric field strength is employed as a physical source for inhomogeneous broadening. A striking result is that a Gaussian probability distribution for the field over the ensemble does not give rise to a Gaussian spectral line shape. The results are used to describe the absorption spectra of the B800 band of the B800-850 light-harvesting complex of photosynthetic purple bacteria.