Asymmetric fitting function for condensed-phase Raman spectroscopy

TL;DR

This paper introduces an asymmetric pseudo-Voigt function for more accurate fitting of asymmetric Raman spectral lines, addressing limitations of symmetric functions and improving data analysis across various condensed matter samples.

Contribution

The paper develops a simple, parameter-efficient asymmetric pseudo-Voigt function based on damped perturbation, suitable for diverse Raman spectra with asymmetries.

Findings

The function accurately fits experimental Raman spectra with various asymmetries.

It provides reliable peak parameters in complex condensed matter systems.

The method is applicable to crystals, nanoparticles, polymers, and liquids.

Abstract

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.