 Because it is not currently known how to adequately correct for nonresonant interferences, it is very important to experimentally isolate the resonant contributions from any nonresonant interference, often done using the technique of nonresonant suppression.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.