Asymmetries of the Voigt line shape

Two cases of asymmetric Voigt line shape are analysed, from which two power series expansions are obtained. In the first case, the line shape is built as a linear combination of the Voigt line shape (VLS) and its derivatives. This is valid for small asymmetries. The second line shape is built as the sum of the VLS and an odd-parity line shape; this second case is valid for intermediate asymmetries. An improved line shape, defined as a linear combination of the traditional VLS with the odd-parity line shape, is also presented. The improved procedure and intermediate case are particularly useful for dealing with X-ray line shapes at lower diffraction angles, as is demonstrated by a practical example.