 The resonating contribution is from the vibrational modes and shows changes in resonance.It can be expressed as a sum of a series of Lorentz oscillators

where formula_30 is the strength or amplitude, formula_31 is the resonant frequency, formula_32 is the damping or linewidth coefficient (FWHM), and each formula_33 indexes the normal (resonant vibrational) mode.The amplitude is a product of formula_34, the induced dipole moment, and formula_35, the polarizability.