Expressions for corrections to spectroscopic intensities can also be identified by a perturbation-theory approach. In a recent work by Bloino and Barone,38 GVPT2 expressions for IR and Raman intensities have been derived. The expression for the IR intensities is30and in classical Raman spectroscopic measurements, the unpolarized (as well as polarized) scattering intensity at a temperature T, related to the Raman cross section, is given by31where32and33where ν i = ω i in the harmonic approximation and is given by eqn (24)–(26) in the anharmonic GVPT2 treatment, ν 0 is the frequency of the incident laser in the Raman experiment, and 0i represents the transition moment of the relevant polarization property from the vibrational ground state to the ith vibrational excited state. In the double-harmonic treatment, these transition moments are determined by first-order geometric derivatives of the polarization property (P 0i1 = ∂P/∂q i), whereas the anharmonic expressions also involve the second- and third-order geometric derivatives of the polarization property and the cubic and quartic force constants. The resulting expressions in the anharmonic case are large and we refer to the work of Bloino and Barone38 where the complete expressions are reported.