The first (second, ...) derivative @A00043@ of a molecule is defined as the first (second, ...) derivative, \(\frac{\text{d}A\left(\overset{˜}{\nu }\right)}{\text{d}\overset{˜}{\nu }}\)[\(\frac{\text{d}^{2}A\left(\overset{˜}{\nu }\right)}{\text{d}\overset{˜}{\nu }^{2}}\), ... ] of the @A00028@ \(A\) as a function of wavenumber, \(\overset{˜}{\nu }\). Wavelengths may be used in place of wavenumbers but the shape of the derivative spectra will be slightly different. When derivative spectra are obtained at low temperature, they are called first (second, ...) derivative @L03638@ (specifying the solvent, temperature and solute concentration).