  Asymmetric lineshapes are experimentally observed in Raman spectra of
different classes of condensed matter. Determination of the peak parameters,
typically done with symmetric pseudo-Voigt functions, in such situations yields
unreliable results. While wide choice of asymmetric fitting functions is
possible, for the function to be practically useful, it should satisfy several
criteria: simple analytic form, minimum of parameters, description of the
symmetric shape as "zero case", estimation of the desired peak parameters in a
straightforward way and, above all, adequate description of the experimental
data. In this work we formulate the asymmetric pseudo-Voigt function by damped
perturbation of the original symmetric shapes with one asymmetry-related
parameter. The damped character of the perturbation ensures by construction the
consistent behavior of the line tails. We test the asymmetric function by
fitting the experimental Raman spectra. The results show that the function is
able to describe a wide range of experimentally observed asymmetries for
different nature of asymmetric broadening, including 3D and 2D crystals,
nanoparticles, polymer, molecular solid and liquid.
